U.S. Department of the Interior

U.S. Geological Survey

MTBE Concentrations in Ground Water in Pennsylvania

by Steven D. McAuley

Water-Resources Investigations Report 03-4201

In cooperation with the

PENNSYLVANIA DEPARTMENT OF ENVIRONMENTAL PROTECTION

New Cumberland, Pennsylvania

2003
ii

U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification purposes only and does not constitute

endorsement by the U.S. Geological Survey.

For additional information Copies of this report may be

write to: purchased from:

District Chief U.S. Geological Survey

U.S. Geological Survey Branch of Information Services

215 Limekiln Road Box 25286

New Cumberland, Pennsylvania 17070-2424 Denver, Colorado 80225-0286

Email: dc_pa@usgs.gov Telephone: 1-888-ASK-USGS

Internet Address: http://pa.water.usgs.gov
iii

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Purpose and scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Description of study area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Approach and methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Sampling strategy and well-selection criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Sampling and data analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Quality-assurance data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

MTBE concentrations in ground water in Pennsylvania . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Sources of MTBE in ground water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Atmospheric concentrations of MTBE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

MTBE detections and concentrations in ground water near known storage-tank

releases and in ambient ground water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Relation of MTBE concentrations to distance from storage-tank release sites . . . . . . . . 13

Occurrence of MTBE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

MTBE detections and concentrations among aquifer types . . . . . . . . . . . . . . . . . . . . . . . 15

MTBE detections and concentrations among land-use categories . . . . . . . . . . . . . . . . . . 15

MTBE detections and concentrations in the Reformulated Gasoline use area . . . . . . . . 20

Areas with frequent MTBE detections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Summary and conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

References cited. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Appendixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

CONTENTS

Page
iv

Figure 1. Map showing distribution of known releases from storage tanks in Pennsylvania,

1988-2001 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2-4. Graphs showing:

2. Mean equivalent aqueous MTBE concentrations calculated from

atmospheric MTBE data at four air-quality monitoring sites in

Pennsylvania, April 2001 to April 2002 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3. MTBE concentrations above the minimum reporting level in near-source

samples and ambient samples and equivalent aqueous MTBE

concentrations calculated from atmospheric data.. . . . . . . . . . . . . . . . . . . 10

4. MTBE detection frequency in near-source and ambient ground-water

samples in Pennsylvania . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

5. Map showing MTBE detection data from all ground-water samples, storagetank release sites, and Reformulated Gasoline use areas in Pennsylvania . . . . 13

6. Graph showing the relation between number of MTBE detections and distance

downgradient of storage-tank releases. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

7. Map showing MTBE detections and major aquifer types in Pennsylvania . . . . . . . 16

8. Graph showing MTBE concentrations and detection frequency by carbonate

rock, crystalline rock, siliciclastic rock, and unconsolidated sediment

aquifer types in near-source and ambient ground-water samples . . . . . . . . . . . 17

9. Map showing MTBE ground-water sample sites and MTBE detections among

land-use categories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

10-11. Graphs showing:

10. MTBE concentrations and detection frequency in agricultural, forest,

and urban land-use categories for near-source and ambient

ground-water samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

11. MTBE concentrations and detection frequency in near-source and

ambient ground-water samples from Reformulated Gasoline

(RFG)-use and non-RFG-use areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

12. Map showing community water system wells near either storage-tank releases

or sample sites with MTBE detections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

ILLUSTRATIONS

Page
v

Table 1. Comparison of MTBE detection frequencies in ground water, minimum

reporting levels, and type and number of samples from studies in

Pennsylvania, Maine, New Jersey, and nationwide for the NAWQA

Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2. MTBE detection frequency in ground water statewide, and by RFG-use,

land-use, and aquifer-type categories. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

APPENDIXES

Appendix 1. Concentrations of MTBE in ambient ground-water samples, in wells near

storage-tank release sites, and in atmospheric samples . . . . . . . . . . . . . . . . . . . 30

2. Equations used to calculate equivalent aqueous MTBE concentration . . . . . . . . . . 44

TABLES

Page
vi

Multiply By To obtain

Length

inch (in.) 25.4 millimeter

foot (ft) 0.3048 meter

mile (mi) 1.609 kilometer

Area

square mile (mi2) 2.590 square kilometer

Flow

gallon per minute (gal/min) 0.06308 liter per second per meter

Flow rate

million gallons per day (Mgal/d) 0.04381 cubic meter per second

Temperature

degree Fahrenheit (°F) °C=5/9 (°F-32) degree Celsius

Other Abbreviations

Abbreviated water-quality units used in this report:

meter (m)

microgram per liter (μg/L)

milliliter (mL)

part per billion by volume (ppbv)

CONVERSION FACTORS AND ABBREVIATED WATER-QUALITY UNITS
1

ABSTRACT

The distribution, concentrations, and detection frequency of methyl tert-butyl-ether

(MTBE), a gasoline additive used in reformulated gasoline to improve air quality, were characterized in Pennsylvania’s ground water. Two

sources of MTBE in ground water, the atmosphere and storage-tank release sites, were

examined. An analysis of atmospheric MTBE

concentrations shows that MTBE detections

(MTBE greater than or equal to 0.2 micrograms

per liter) in ground water are more likely the

result of storage-tank releases than atmospheric

deposition. A comparison of 86 ground-water

samples near storage-tank releases and

359 samples from ambient ground water (not

thought to be affected by point-source releases of

MTBE or BTEX compounds) shows that samples

within about 0.5 mile downgradient of storagetank release sites have significantly greater

MTBE detection frequency than ambient

ground-water samples.

Aquifer type, land use, and the use of Reformulated Gasoline (RFG) are associated with

high rates of occurrence of MTBE in ground

water in Pennsylvania. Ground-water samples

from wells in crystalline-rock aquifers near storage-tank release sites have a significantly

greater MTBE detection frequency (57 percent)

compared to other aquifers. Samples from wells

in urban areas have a significantly greater

MTBE detection frequency compared to ambient

samples in agricultural and forested areas. Samples from the RFG-use areas in the five southeastern counties of Pennsylvania have a

significantly greater MTBE detection frequency

than samples outside of the RFG-use area.

MTBE detection frequency of samples near storage-tank release sites in the RFG-use area

(45 percent) are significantly greater than ambient samples in the RFG-use area.

INTRODUCTION

Methyl tert-butyl-ether (MTBE) is a synthetic chemical that has been added to gasoline

since 1979 as an octane enhancer to replace lead.

The Clean Air Act Amendments of 1990 created

the Oxygenated Fuels Program and the Reformulated Gas Program to add oxygen to gasoline

in areas that do not meet National Ambient Air

Quality standards for carbon monoxide and

ozone. In the mid-1990s, MTBE began to be used

as an oxygenate (referred to as an oxyfuel) to

reduce carbon monoxide, and as part of Reformulated Gasoline (RFG), to reduce ground-level

ozone in many areas of the Nation. The RFG

Program, begun in 1995 in many Northeastern

and Mid-Atlantic States, requires that gasoline

sold throughout the year in the areas having the

highest levels of tropospheric ozone must contain a minimum of 2 percent oxygen by weight.

The program does not specify which oxygenate

must be added to gasoline to meet the standard,

but MTBE commonly is used. The use of RFG

lowers the emissions of unburned aromatic compounds and therefore the formation of ozone in

air. In areas where MTBE is used in RFG or in

oxyfuel, MTBE commonly constitutes

10–15 percent of the gasoline by volume

(Johnson and others, 2000). To meet the requirements of the Clean Air Act Amendments, gasoline in RFG areas must contain 11 percent

MTBE by volume (if MTBE is the oxygenate

used).

RFG is used in the five southeastern counties of Pennsylvania (Bucks, Chester, Delaware,

Montgomery, and Philadelphia) to reduce

ground-level ozone (fig. 1). In all other areas,

including the Pittsburgh area, where Reid Low

Vapor Pressure gasoline is used to combat ozone

concerns, smaller amounts of MTBE (generally

about 1 percent or less) are used in most gasoline, usually as an octane booster.

Thousands of releases of petroleum products

(mostly gasoline) from storage tanks, above and

below ground, have been reported in Pennsylvania (Stuart Reese, Pennsylvania Department of

Environmental Protection, written commun.,

MTBE CONCENTRATIONS IN GROUND WATER IN PENNSYLVANIA

by Steven D. McAuley
2

2001). Nationally, 330,000 point-source releases

from leaking underground storage tanks have

been reported to U.S. Environmental Protection

Agency (USEPA) (Moran and others, 1999).

MTBE can move into the ground water from

point sources such as a leaking storage tank or

petroleum pipeline (above or below ground),

from spills or evaporative losses at refueling stations, from vehicle accidents, or from homeowner

releases. MTBE also can move into the ground

water from nonpoint sources such as vehicle

emissions, atmospheric deposition (especially via

infiltration of precipitation), and urban stormwater runoff (U.S. Environmental Protection

Agency, 1999; National Science and Technology

Council, 1997). MTBE, unlike benzene, is very

soluble in water, very mobile in ground-water

systems, and more resistant to biodegradation

than the toxic gasoline components benzene, toluene, ethyl benzene, and xylene (referred to as

BTEX compounds). Because of these properties,

MTBE plumes can spread for kilometer-scale

distances (several thousand feet to miles) in the

subsurface. Because of its use as an octane

booster, MTBE may be found in ground water at

or near any leaking underground storage tank in

the United States, even in areas where MTBE is

not used to meet RFG or oxyfuel requirements.

Figure 1. Distribution of known releases from storage tanks in Pennsylvania, 1988-2001. (Data from Storage Tanks

Division of Pennsylvania Department of Environmental Protection.)
3

During the 1990s, MTBE was detected in

5 percent or more of private or public drinking

water supplies nationally, and the percentage of

MTBE detections was greater than 5 percent in

high-MTBE-use areas (Zogorski and others,

2001; National Science and Technology Council,

1997)1. Although most of the detections nationally were at low (<20 μg/L) concentrations,

1 percent of MTBE concentrations were above

the USEPA Consumer Advisory threshold of

20 μg/L. MTBE has been reported in ground

water at concentrations as high as 200,000 μg/L

near releases from storage tanks (National Science and Technology Council, 1997).

The USEPA Consumer Advisory recommends MTBE control levels of 20 to 40 μg/L to

prevent adverse odor and taste (U.S. Environmental Protection Agency, 2003). These levels

are not enforceable legally. Human-health

effects from MTBE remain uncertain; however,

USEPA tentatively has classified MTBE as a

possible human carcinogen but, because of insufficient toxicity studies, has not instituted a

drinking-water health advisory (Zogorsky and

others, 2001).

Pennsylvania relies heavily on ground water

for public drinking-water supplies. In 1995,

about 243 Mgal/d of ground water were used for

drinking-water supply, which constitute

15.7 percent of all water used for public drinking

water in Pennsylvania. The combined populations served by (1) community systems with

ground water as a primary source of drinking

water; (2) community systems with at least one

ground-water source; and (3) private on-lot wells

account for nearly half of the population of Pennsylvania (P. Bowling, Pennsylvania Department

of Environmental Protection, written commun.,

2002). Ground water, commonly the principal

source of drinking water in most rural areas and

an important source in some urban areas, continues to be a principal source of drinking water

in areas where urban development recently has

increased. Increased development in urban

areas results in increased use of gasoline storage

tanks and refueling gas stations. Recent reports

in Pennsylvania of MTBE in ground water used

for drinking-water supply have raised concerns

of citizens and water-resource managers. Many

private wells in the five southeastern Pennsylvania counties and, to a lesser extent, in other

areas of Pennsylvania, have been contaminated

by MTBE, as indicated in numerous reports of

investigations of MTBE contamination, overseen

by or submitted to the Pennsylvania Department

of Environmental Protection (PADEP) (Pennsylvania Department of Environmental Protection,

various staff, oral commun.), and newspaper

articles.

Because of concerns over concentrations of

MTBE in ground water, PADEP and the U.S.

Geological Survey (USGS) initiated a cooperative study to assess the distribution and concentrations of MTBE in ground water used for water

supply, to compare the concentrations of MTBE

to drinking-water standards or advisories, and to

determine whether there are factors associated

with high rates of occurrence of MTBE in ground

water. The PADEP is interested in determining

if there are certain areas or aquifers that are

more susceptible to MTBE or that have greater

concentrations of MTBE to assist in targeting

the PADEP sampling program for MTBE in

drinking-water wells and in prioritizing storagetank inspections. The USGS is interested in adding to the knowledge of the occurrence of MTBE

in ground water.

Purpose and Scope

This report (1) examines sources of MTBE in

ground water from atmospheric deposition and

near release sites and compares the concentrations and frequency of detection of MTBE in

ground water from wells topographically downgradient of known release sites to wells in areas

where the location of release sites is not known

or release sites may not exist, and (2) examines

the MTBE concentrations and frequency of

detection in aquifers across Pennsylvania,

among land uses, and in the RFG-use area. In

each case, MTBE concentrations near release

sites are compared to MTBE concentrations in

ambient ground water (ground water that is not

thought to be associated with point-source

releases of MTBE or BTEX compounds). Finally,

areas at risk for high detection frequencies of

MTBE are identified.

1 The results reported in Zogorski and others

(2001) are a synthesis of results from individual study

units in the U.S. Geological Survey National WaterQuality Assessment Program. Study-unit reports that

include MTBE analysis are available at

http://wwwsd.cr.usgs.gov/nawqa/vocns

or at http://water.usgs.gov/nawqa
4

During this study, MTBE data from previous

USGS studies in Pennsylvania between 1993

and 2001 were compiled and interpreted. A total

of 359 wells across Pennsylvania were sampled

for MTBE during these previous studies. These

samples were collected to meet the objectives of

the previous studies and therefore were not

equally distributed statewide. In addition, no

areas near release sites were targeted for sampling.

As part of the current study, samples from

86 wells were collected during June 2001

through February 2002. To fill in the data gap

from the previously collected samples, all the

86 wells are within about 0.5 mi of a storagetank release and are downgradient of the release

site, as indicated by topographic contours.

Although an attempt was made to sample

equally from the areal extent of each of the

major aquifer types in Pennsylvania, samples

were not collected in some areas because the

release sites are not distributed evenly across

the state, and neither is use of ground water for

drinking-water supplies. The density of the

release sites is greatest in urban areas but there

are release sites throughout much of Pennsylvania (fig. 1).

Description of Study Area

The climate of Pennsylvania is temperate.

The statewide mean annual precipitation ranged

from 35 to 40 in. during 1971 to 2000. During

1971 to 2000, the wettest month was June, and

the driest month was February. The statewide

mean annual temperature ranged from 45 to

50°F during this same period (National Oceanic

and Atmospheric Administration, 2003).

Pennsylvania has a diverse distribution of

geology (Schultz, 1999). Ground water from most

of the geologic formations is used for water supply. Aquifers across the state of Pennsylvania

were classified into four generalized types:

(1) crystalline rock, (2) carbonate rock, (3) siliciclastic rock, and (4) unconsolidated sediments,

after Lindsey and Bickford (1999). The unconsolidated sediments include alluvium, glaciofluvial

deposits, and deposits in the Cretaceous Coastal

Plain near Philadelphia.

Three major land uses in Pennsylvania—

urban, agricultural, and forested—account for

most of the land area of the state. Pennsylvania

has vast areas dominated by forested land use

(about 65 percent) and substantial areas dominated by agricultural land use (about 28 percent). Urban areas account for only about

4 percent of the state area. The remainder of the

state area is covered by water or wetlands (about

2 percent) or by transitional, mining, or barren

areas (about 1 percent).

Urban areas in Pennsylvania, although having only a small percentage of the total land

area, have the greatest number of vehicles and,

subsequently, the greatest number of refueling

stations. Counties with large urban areas have

the greatest number of registered passenger

vehicles in Pennsylvania. The 20 counties with

the greatest number of registered passenger

vehicles all include large metropolitan or urban

areas within or near to their boundaries. The

five counties that compose the RFG-use area are

the second, third, fourth, fifth, and seventh highest ranking of 67 counties in terms of number of

registered passenger vehicles in the state in

2002 (Kurt Myers, Pennsylvania Department of

Transportation, written commun., 2003). In fact,

nearly 28 percent of the more than 7.4 million

registered passenger vehicles in the state are

registered in the five counties of the RFG-use

area.

Acknowledgments

The author thanks the 86 well owners for

permitting the USGS to sample their wells and

the Air Quality Bureau of PADEP for providing

atmospheric MTBE concentration data. Connie

Loper, Andrea von der Pfordten, Donald Williams, Mary Clark, Elaine Gee, Dennis Low,

Theodore Buckwalter, and Mark Henneberg, all

of USGS, are thanked for their assistance with

identification of wells that met the sampling criteria. Connie Loper, Andrea von der Pfordten,

and Donald Williams also are thanked for their

assistance with the sampling and sample-processing effort. Scott Hoffman of USGS produced

the Geographic Information System coverages

needed to make maps for the report, and James

Bubb, Terriann Preston, and Leona McLanahan,

also of USGS, helped with the preparation of

illustrations and text for the report. Stuart

Reese and Douglas Cordelli of PADEP were

helpful in providing PADEP data on releases.

The following reviewers are thanked for

their helpful comments and suggestions: Kim

Otto, Dennis Risser, Edward Koerkle, Dennis
5

Low, Eric Vowinkel, Patricia Lietman, and

Ronald Sloto of the USGS, and Joseph Lee,

Patrick Bowling, Douglas Cordelli, and Robert

Day-Lewis of the PADEP.

APPROACH AND METHODS

Sampling Strategy and Well-Selection Criteria

Data collected as part of several projects conducted by the USGS in Pennsylvania during

1993-2001 were compiled (table 1A)1. Sampling

sites for all previous samples collected in Pennsylvania for the National Water-Quality Assessment Program (NAWQA) had been determined

by a stratified random process and were

designed to examine ambient ground water.

Wells near known releases of petroleum products were not targeted for sampling in other previous studies. Usually, the ground water of an

area or of a particular aquifer was the target of

the study. The data from other USGS studies in

Pennsylvania are referred to as ambient groundwater samples in this report. In a few cases, the

data may not be truly ambient because the samples were collected from wells used to monitor

for non-MTBE and non-BTEX contaminants. To

complement the ambient MTBE data, water

samples were collected as part of this study from

wells near storage-tank release sites and analyzed for MTBE during July 2001 through

February 2002 (table 1B). The sampling network

was designed to examine MTBE distribution and

concentration near known source locations and

to compare those concentrations to ambient

ground-water concentrations.

An effort was made to collect samples from

an equal number of wells from each of the four

different types of aquifers in the state. The areal

extent of each aquifer was divided into subareas

and one or two wells were sampled from each

subarea if wells that met the criteria could be

located.

To be selected for sampling, a well had to be

within about 0.5 mi and topographically downgradient from a known release site. Well depths

of 250 ft or less were preferred, but if data such

as geologic logs showed that water-bearing zones

were less than 250 ft deep, that also was acceptable. The depth criteria was used to focus on

shallow water-supply wells. A few wells

exceeded the depth criteria but were sampled

because of difficulty in locating wells in some

areas. Well depths were reported by well owners

or drillers. Wells used to monitor releases were

not sampled. Wells with low yields (<50 gal/min)

were preferred, but some higher-yielding wells

were sampled. Only untreated water from wells

was sampled, and no springs were sampled.

The locations of known release sites in Pennsylvania from about 1988 to 2001 were acquired

from the PADEP Storage Tank Division. The

release sites did not have latitude and longitude

coordinates, only addresses. Because geo-referencing software was used on the addresses to

determine latitude and longitude, the accuracy

of this determination is dependent on the accuracy of the address. Although data on about

15,000 storage-tank releases were stored in the

PADEP database, only about 7,000 had

addresses with sufficient information for the

software to calculate a latitude and longitude

accurate enough for the location to be found in

the field by USGS personnel, if necessary. The

location accuracy was determined to be either an

exact location or a location known to within a

few hundred feet.

Data from the PADEP database on storagetank releases originally contained only location

of the storage-tank release, brief information or

no information about the contaminant, and no

information about the existence of nearby wells

used for drinking water. Information about the

age, mass, and contaminant plume extent is not

in the database. Not all storage-tank releases

were identified as containing benzene, gasoline,

or MTBE; instead, there may have been some

releases of home heating oil. The type of contaminant reported was not taken into account when

the sampling effort began, so some sites sampled

could have been near heating-oil releases,

though these releases are a small percentage of

the total releases documented in the database.

The great majority of the releases were labeled

as releases from gas stations or releases with

benzene, gasoline, or MTBE listed as the contaminant.

Initially, the search for qualified wells near

release sites was not very successful. Subsequently, a revised PADEP database was compiled that included only release sites where

1 Data collected by the USGS also are available in

the USGS National Water Information System (NWIS)

computer databases at

http://waterdata.usgs.gov/nwis/
6

MTBE had been reported and where PADEP

investigators reported wells used for water supply within about 0.5 mi of the release site. Using

this revised database enabled greater success of

locating wells that met sampling criteria. Nearly

80 percent of the 86 wells sampled were located

using the revised database.

The MTBE data may be biased or not agree

with data in the PADEP database of release sites

for several reasons.

1. Where sampling was done near a release

site without confirmed MTBE, no MTBE

might have been present. However, the

listing of contaminants in the release

database is not complete or accurate.

2. At some release sites, the database may

list heating oil as the source contaminant

but MTBE could be present because of

cross contamination during transportation (Hinchey and others, 2001).

3. At older release sites, MTBE was not analyzed for but may have been present.

4. MTBE will almost always be present near

the release sites because of its use in most

gasoline, but remediation may have

removed the MTBE prior to sampling for

this study.

Sampling and Data Analysis

The sample plan was designed to locate

about 30 samples from each of 4 aquifer rock

types in Pennsylvania. Poor success in finding

suitable wells in some areas resulted in an

unequal number of samples for the four aquifers.

The final distribution of samples by aquifer type

was 21 samples from the carbonate-rock aquifers, 21 samples from the crystalline-rock aquifers, 28 samples from the siliciclastic-rock

aquifers, and 16 samples from the unconsolidated sediments.

Parts per billion sampling protocols

described by Koterba and others (1995) were followed but modified for several factors such as

one-person sampling where possible, sampling

from high volume supply wells, and sampling

only for MTBE and BTEX compounds and

selected field constituents (temperature, specific

conductance, and pH). The modifications do not

affect any results or laboratory analyses because

the modifications were made to protocols written

for sampling nonvolatile organic compounds

(such as pesticides) or trace metals. The current

study called for sampling only MTBE and BTEX

compounds. One of the modifications permitted

the use of copper fittings and tubing, instead of

teflon, to connect to water sources. The procedures used were discussed with and agreed to by

members of the NAWQA VOC Team. Clean,

parts per billion sampling protocols significant

to sampling VOCs were followed.

Most commonly, the well owner’s pump provided the sample water when a satisfactory tap

into the plumbing could be located. A low volume

sampling pump was used to obtain the water

sample from a few wells. After monitoring pH,

specific conductance, and temperature until

readings were stable, the unfiltered samples

were collected from untreated well water into

completely full (no entrapped air bubbles) 40-mL

glass vials, chilled, and sent to the laboratory.

The minimum reporting level (MRL) for

MTBE used by the USGS laboratory is different

among the ambient samples. To analyze all the

samples, a common MRL had to be selected. For

this study, 0.2 μg/L was selected. Any data

reported at concentrations below 0.2 μg/L were

considered to have MTBE concentrations of

<0.2 μg/L for this study. Any data reported at an

MRL greater than 0.2 μg/L were eliminated from

the data set. Very few samples (7 of 366 samples)

had an MRL greater than 0.2 μg/L.

The 86 samples collected were analyzed at

the USGS National Water Quality Laboratory

near Denver, Colo., using purge and trap gas

chromatography/mass spectrometry (GC/MS)

methods (Rose and Schroeder, 1995). These

methods are comparable to USEPA method

524.2 (U.S. Environmental Protection Agency,

1992).

Categorical methods were used to perform

statistical analysis with groups of the data

(Helsel and Hirsch, 1992). More than 50 percent

of the data were below the MRL of 0.2 μg/L, rendering analysis of data with statistical tests

based on means or medians infeasible. The number of detections and nondetections were compared, and a Kruskal-Wallis test for ordered

categorical responses was conducted. The data

are ordinal in that the response variable, MTBE

concentration, is listed only as either above the

MTBE MRL for this study (an MTBE detection)

or below the MRL (an MTBE nondetection). The

procedure includes a ranking of the data where

all detections are tied in ranking and all nonde-
7

tections are tied in ranking. As used in the analysis for this study, the test determines whether

groups or categories, such as land use or aquifer

types, etc., are found to have significantly different proportions of detections to nondetections of

MTBE. The proportions are then expressed as

percentages, or as frequency of MTBE detection

expressed as a percentage. An alpha of 0.05

(95-percent confidence level) was used as the significance level of the statistical tests.

Some of the categories used for statistical

analysis contained multiple subcategories; for

example, the land-use category consists of subcategories for urban area, agricultural area, and

forested area. If a significant difference was

found in detection frequency for one or more subcategories, a determination of which subcategories differ from others was made by performing

multiple comparisons with Kruskal-Wallis tests

between groups of subcategories until all subcategories that are significantly different from

other subcategories are identified (Helsel and

Hirsch, 1992).

Quality-Assurance Data

The sampling effort included a qualityassurance (QA) plan to evaluate any bias or contamination issues in the samples. Thirteen QA

samples were analyzed, which included two

equipment blanks, two trip blanks, two field

blanks, four replicate samples, and three field

spikes.

Blanks are used to assess bias in environmental samples because of contamination.

Equipment blanks were collected in a controlled

environment (the District laboratory) prior to

initial sampling to assure that equipment is contaminant-free after cleaning. Equipment

includes fittings and tubing used to collect samples. Both equipment blanks showed no detection of MTBE or BTEX compounds at the

0.2 μg/L MRL. Trip blanks were never opened in

the field and were intended to measure any contamination during sample transport. Both trip

blanks showed no detection of MTBE or BTEX

compounds. Field blanks also measure contamination, and the two field blank samples showed

no detections of MTBE or BTEX compounds.

For replicate samples, the concentrations of

MTBE and BTEX compounds were below the

MRL in the environmental and the replicate

samples.

Two field spikes showed recoveries of

91 percent and 86 percent. The favorable recoveries of field spikes indicate good precision in the

sample analysis.

MTBE CONCENTRATIONS IN GROUND

WATER IN PENNSYLVANIA

Atmospheric deposition (nonpoint source)

and releases from storage tanks (point sources)

are significant sources of MTBE in ground water

in Pennsylvania. MTBE concentrations and frequency of detection were examined to determine

if certain aquifers, land uses, or RFG uses are

associated with high occurrence of MTBE.

Sources of MTBE in Ground Water

Nonpoint and point sources contribute

MTBE to ground water. Nonpoint sources

include atmospheric deposition, particularly

from precipitation; vehicle exhaust emissions;

and stormwater runoff (National Science and

Technology Council, 1997). Point sources include

storage-tank (above or below ground) releases,

overfilling gas tanks at gasoline stations, vehicle

accidents, pipeline releases, refinery releases,

watercraft engine releases, homeowner spills,

and evaporative losses at refueling.

Atmospheric Concentrations of MTBE

Atmospheric deposition is one of the most

likely nonpoint sources for MTBE. Low concentrations in ground water are considered to be the

result of atmospheric deposition of MTBE that

infiltrates the unsaturated zone and travels to

the water table (Baehr and others, 1999, 2001;

Zogorski and others, 1998). Infiltration and dispersion can transport MTBE from the air into

the unsaturated zone and into the ground water

(Pankow and others, 1997).

In a study in southern New Jersey of the

atmosphere as a source of VOCs in shallow

ground water, Baehr and others (1999, 2001)

used atmospheric concentrations of MTBE to

calculate concentrations of MTBE in equilibrium

with aqueous phase MTBE concentrations and

to assess the relevance of atmospheric concentrations of MTBE to ground-water quality. They

observed that mean atmospheric MTBE levels

near Glassboro, N.J., equated to about 0.1 μg/L

when converted to equivalent aqueous MTBE

concentrations. The MRL for the MTBE in the
8

atmosphere was 0.05 ppbv in the New Jersey

study. The wells sampled in the New Jersey

study are all shallow monitor wells that tap into

unconsolidated sediments in an RFG-use area.

Atmospheric MTBE data are examined in

this report to estimate MTBE in ground water

contributed by atmospheric deposition and to

determine whether MTBE concentrations less

than 20 μg/L are likely from atmospheric (nonpoint) sources. The PADEP Bureau of Air Quality collects atmospheric MTBE data at some of

the air-quality monitoring sites in Pennsylvania

(Ralph Scanlon, Pennsylvania Department of

Environmental Protection, written commun.,

March 2001). Atmospheric MTBE data were

obtained from PADEP air-quality monitoring

sites at Pittsburgh, Lancaster, West Chester, and

Arendtsville, Pa. (Gary LaBelle, Pennsylvania

Department of Environmental Protection, written commun., July 2002) (table 1C). Data from

the four sites were used to determine the data

distribution and an approximate regional value

of atmospheric MTBE for Pennsylvania. The

time period over which the samples were collected varies from site to site; however, data

were used for this report from Pittsburgh (during 4/01/01–12/21/01), Lancaster (during

4/01/01–3/31/02), West Chester (during 4/01/01–

12/3/01), and Arendtsville (during 5/13/01–

3/31/02) (table 1C). Other time periods for these

four sites and one other sample location

(Presque Isle in Erie County) were not used

because of problems identified in the data sets

(Gary LaBelle, Pennsylvania Department of

Environmental Protection, written commun.,

July 2002). The atmospheric data consist of

results of analysis of 24-hour composite samples

collected every 6 days. The detection level used

in this analysis of the data from the air-quality

sites for the above time periods ranged from 0.01

to 0.02 ppbv. These time periods provide nearly

three-fourths of a year of data for two sites and

nearly a year of data for two sites. Three of the

sites are in urbanized areas (Pittsburgh, West

Chester, and Lancaster) and one site is in a rural

setting (Arendtsville, 10 mi north of Gettysburg,

Pa.) (fig. 1). The Lancaster and West Chester

sampling sites are in a parking lot for a school

and therefore may not be representative of the

air everywhere in Lancaster and West Chester.

The method described by Baehr and others

(1999) was used to calculate the equivalent

aqueous MTBE concentrations from atmospheric

MTBE data and temperature collected at the

four sites in Pennsylvania (Appendix 2). The

temperature data were obtained from a PADEP

air-quality monitoring site where available and

from the nearest National Oceanic and Atmospheric Administration (NOAA) air-quality sites

elsewhere (Harrisburg for Arendtsville as

needed and Philadelphia for West Chester as

needed). Equivalent aqueous MTBE concentrations vary across Pennsylvania as measured by

the PADEP air-quality monitoring sites. The

mean equivalent aqueous MTBE concentration

for the period of available data for West Chester

(0.12 μg/L) was at least three times greater than

the means for the other sites (Arendtsville,

0.01 μg/L; Pittsburgh, 0.03 μg/L; Lancaster,

0.04 μg/L) (fig. 2). Of the four sites, West Chester

is the only air-quality monitoring site in the

RFG-use area. The higher use of MTBE in that

area likely results in greater atmospheric levels

of MTBE.

All MTBE detections in ground water presented in this report are above the calculated

mean equivalent aqueous MTBE concentrations

in the atmosphere and, therefore, are unlikely to

be solely the result of atmospheric deposition of

MTBE (fig. 3). Instead, they are most likely from

the point sources sampled near releases and

other types of point sources. Certainly, some

MTBE detections may be the result of atmospheric input in whole or in part. Atmospheric

MTBE levels do vary in time and space. The

samples with MTBE reported at the MRL

(0.2 μg/L) could be from either nonpoint (atmospheric) sources or from point sources or a combination. The MTBE concentrations are

censored above the level needed to compare

ground-water data to atmospheric MTBE data to

determine more exactly if there is a concentration lower than 0.2 μg/L at which the groundwater samples are likely from point sources.

Based on available atmospheric MTBE data for

Pennsylvania, ground-water samples with

MTBE concentrations of 0.2 μg/L or greater are

likely from point sources.

Baehr and others (1999) stated that many of

the MTBE detections in ground water in New

Jersey could be the result of atmospheric input;

however, the MTBE MRL for ground-water samples for his study was 0.1 μg/L, which was equal

to the 50th percentile of the equivalent aqueous

atmospheric MTBE data. The lowest reported

MTBE concentration in the current study
9

Figure 2. Mean equivalent aqueous MTBE concentrations calculated from atmospheric MTBE data at four airquality monitoring sites in Pennsylvania (Arendtsville, Lancaster, Pittsburgh, and West Chester), April 2001 to

April 2002. (Minimum reporting level ranges from 0.01 to 0.02 ppbv.)
10

(0.2 μg/L) is equal to about the 77th percentile of

the atmospheric data (in equivalent aqueous

concentration) from West Chester, which has the

highest mean atmospheric levels and is in the

RFG-use area (fig. 3). The median equivalent

aqueous concentration of MTBE calculated from

the West Chester data, 0.05 μg/L, is much less

than the median MTBE concentration of

0.4 μg/L for the samples that are above the MRL

(MTBE detections) in near-source samples and

the median MTBE concentration of 0.5 μg/L for

the ambient samples above the MRL.

The effect of attenuation can further demonstrate that the MTBE concentrations above the

MRL in ground water are not likely the result of

atmospheric deposition of MTBE. The calculations of equivalent aqueous MTBE concentrations from the atmosphere do not take into

account the attenuation that may occur during

transport through the unsaturated zone. Thus,

the contribution of atmospheric MTBE to ground

water may be less than shown in the current

study by calculations of equivalent aqueous

MTBE concentrations. Baehr and others (1999)

have concluded that residence time of the atmospheric MTBE in the unsaturated zone and temperature effects can decrease the amount of

MTBE that reaches the zone of saturation and

may result in nondetects of MTBE in ground

water, even though the atmospheric data show

that MTBE is present. In addition to dilution

from mixing, adsorption, biotic and abiotic transformation, and volatilization (Buxton and others, 1997), MTBE can be attenuated by

Figure 3. MTBE concentrations above the minimum reporting level in near-source samples and ambient

samples and equivalent aqueous MTBE concentrations calculated from atmospheric data. (The minimum

reporting level is 0.2 μg/L for ground-water samples and ranges from 0.01 to 0.02 ppbv for atmospheric

samples.)
11

remediation efforts. If the concentrations of

MTBE in ground water that exceed the MRL, as

examined in this study, were attenuated from

MTBE concentrations that were contributed

originally and directly, as by point source, to the

unsaturated zone and the ground-water system,

then the difference between pre-attenuated concentrations of MTBE in ground water and atmospheric MTBE concentrations would be greater

than shown in the current study.

MTBE Detections and Concentrations in

Ground Water Near Known Storage-Tank

Releases and in Ambient Ground Water

MTBE was detected more frequently in nearsource samples compared to ambient samples,

indicating that releases are a significant source

of MTBE in ground water. MTBE was detected

in 22 percent of near-source samples compared

to 11 percent of ambient samples (fig. 4 and

table 1). The Kruskal-Wallis test results indicate

a significant difference between the near-source

samples and the ambient samples. The detection

frequency of near-source samples is significantly

greater than the detection frequency of the

ambient samples.

The MTBE concentrations observed in this

study are at low levels. Only one near-source

sample and one ambient sample exceeded the

USEPA Consumer Advisory threshold of

20 μg/L. MTBE concentrations ranged from

0.2 to 31 μg/L for near-source samples and from

0.2 to 51 μg/L for ambient samples (fig. 3). The

median concentrations of all near-source samples and all ambient samples are both equal to

the MRL. Median concentrations of samples

above the MRL were 0.4 μg/L for near-source

samples and 0.5 μg/L for ambient samples.

The MTBE detection frequency in nearsource samples in this study (22 percent) is

higher than those in ambient samples in two

other studies with similar MRLs (table 1). The

MTBE detection frequency for ambient samples

from the USGS NAWQA Program (5 percent) is

less than the detection frequency for ambient

Figure 4. MTBE detection frequency in near-source and ambient groundwater samples in Pennsylvania. (The minimum reporting limit is 0.2 μg/L.)
12

samples for this study (11 percent). The MRL is

0.2 μg/L for both data sets (Zogorski and others,

2001). A study in Maine (State of Maine, 1998)

and a study in New Jersey (Stackelberg and

others, 1997) showed higher MTBE detection

frequencies for ambient samples than the

current study, but the MRL for both those

studies was 0.1 μg/L. The ambient ground-water

sources sampled in Maine included springs, dug

wells, and drilled wells.

The data suggest that the likelihood of

detecting MTBE is significantly greater when

sampling near known releases than the likelihood of detecting MTBE in ambient ground

water. Two factors may explain low MTBE concentrations in samples collected at near-source

sites.

1. Attenuation of MTBE concentrations will

likely occur over time. The time and mass

of contaminant released is not known for

many release sites, but if the release happened several years prior to collection of

the sample for this study, MTBE concentrations likely were once greater than

reported here because of attenuation.

MTBE tends to attenuate naturally at the

half-life rate ranging from 0.2 to 2.2 years

in the unsaturated zone in unconsolidated

sediments in New Jersey (Baehr and others, 1999). Data from other studies have

shown a similar range of MTBE half-life

(U.S. Environmental Protection Agency,

1999). Remediation efforts also could

reduce the MTBE concentrations over

time.

2. The well may be near the edge of a MTBE

plume. In this case, either intermittent

pumping of the domestic well results in

capturing low concentrations of MTBE or

domestic wells distant (>1,000 ft) from

the release could contain low concentrations of MTBE (<20 μg/L) that are not

affected by a remediation effort. MTBE

remediation efforts tend to focus on high

MTBE concentrations (>20 μg/L) near the

release site. Distant wells may not get

sampled for MTBE unless a complaint is

received from well owners or basement

owners.

Table 1. Comparison of MTBE detection frequencies in ground water, minimum reporting levels, and

type and number of samples from studies in Pennsylvania, Maine, New Jersey, and nationwide for the

NAWQA Program

Study

MTBE in

ground water in

Pennsylvania

MTBE in

ground water in

Pennsylvania

NAWQA

Program1

Maine

study2

New

Jersey

study3

Type of samples: Near-source

samples

Ambient

samples4

Ambient

samples5

Ambient

samples5

Ambient

samples5

MTBE detection frequency

(in percent)

22 11 5 16 45

Minimum reporting level

(micrograms per liter)

.2 .2 .2 .1 .1

Number of samples 86 359 thousands 946 72

1 Zogorski and others, 2001.

2 State of Maine, 1998.

3 Stackelberg and others, 1997.

4 Samples considered ambient with regard to MTBE concentrations.

5 Samples are selected randomly and assumed to be ambient.
13

Relation of MTBE Concentrations to Distance

From Storage-Tank Release Sites

The 86 near-source samples were collected at

distances up to about 0.5 mi downgradient from

a known release (fig. 5).

The number of MTBE detections decreases with

increased distance from a release (fig. 6). The

number of detections of MTBE decreases from

8 of 20 samples within 500 ft of a release, to 6 of

28 samples from 501 to 1,000 ft from a release,

to 2 of 15 samples from 1,001 to 1,500 ft from a

release, to 1 of 11 samples from 1,501 to 2,000 ft

from a release, to 2 of 12 samples beyond 2,000 ft

of a release. The number of nondetection

sampling points seems to be distributed

relatively evenly throughout the distance from

releases. It should be made clear that these

samples are collected near 86 different release

sites and do not represent the decrease that may

be expected in a particular plume of MTBE.

Figure 5. MTBE detection data from all ground-water samples, storage-tank release sites, and Reformulated

Gasoline use areas in Pennsylvania. (The minimum reporting limit is 0.2 μg/L.)
14

Figure 6. The relation between number of MTBE detections and distance downgradient of storage-tank

releases. (The minimum reporting limit is 0.2 μg/L.)
15

The relation between the MTBE concentration and distance from a release can be affected

by the sample location in a MTBE plume and

MTBE attenuation depending on the time

elapsed since the release. Decreasing MTBE

detections with increasing distance from a

release for the 86 samples at 86 different release

sites lends some additional support to the

hypothesis that the detections are the result of

point sources.

The properties of MTBE permit long-range

transport (Moran and others, 1999, Buxton and

others, 1997). MTBE can be transported farther

and deeper than BTEX compounds. Very few

detections of BTEX compounds have been found

concurrently with MTBE in ambient samples

collected as part of the NAWQA Program (Zogorski and others, 1998). Although the BTEX data

are not presented in this report, only 1 of

86 near-source samples had concurrent detections of BTEX compounds and MTBE. The lack

of co-occurrence of MTBE and BTEX compounds

may be associated with the high solubility and

mobility and low biodegradation properties of

MTBE relative to BTEX compounds, which

results in detection of MTBE, but not BTEX

compounds, at distal portions of gasoline contaminant plumes (Grady and Casey, 2000).

Occurrence of MTBE

MTBE Detections and Concentrations

Among Aquifer Types

This study was designed to permit sampling

of an equal number of wells, if possible, in each

of the four generalized aquifer types in Pennsylvania (fig. 7). Given the uncertainties in locating

wells near known release sites, the results of the

sampling yielded different numbers of samples

in each of the four aquifer types, but the differences are not considered too great to make comparisons among the aquifer types. Twenty-one

samples were obtained from carbonate-rock

aquifers, 21 samples were obtained from crystalline-rock aquifers, 28 samples were obtained

from the siliciclastic-rock aquifers, and

16 samples were obtained from unconsolidated

aquifers.

Results from the Kruskal-Wallis statistical

tests show that the frequency of MTBE detections in near-source crystalline-rock aquifer

samples is significantly greater (57 percent)

than either near-source or ambient samples from

any other aquifer type. The two greatest frequencies of detections are in samples from the

crystalline-rock aquifer (fig. 8); however, the

detection rate from ambient samples from the

crystalline-rock aquifer is not significantly different from detection frequencies in any other

aquifer except the near-source crystalline-rock

aquifer samples and the ambient siliciclasticrock aquifer samples.

Properties of the crystalline-rock aquifers,

and the low permeability of the overlying saprolite, may slow movement of MTBE plumes and

lessen dilution and dispersion, resulting in

MTBE being transported at a slow rate and

therefore remaining near a release site for a

longer time than it would in areas without

saprolite.

It is also possible that physical properties of

the crystalline-rock aquifer may not be reasons

for higher MTBE detection rates. The percentage of the total areal extent of the crystallinerock aquifer in Pennsylvania that underlies the

RFG area (40 percent) is much greater than the

percentages of extents of the other aquifers that

underlie the RFG area (3, 3, and 12 percent for

the carbonate rock, siliciclastic rock, and unconsolidated sediments aquifer types, respectively).

Determination of the effects of physical properties of an aquifer on the extent and fate of a

plume of MTBE would require detailed site-specific hydrogeologic information for many release

sites and a study of the transport of MTBE over

time at many sites. Aquifers with higher permeability, such as unconsolidated sediments,

showed a lower frequency of detection, perhaps

indicating greater movement of MTBE. Aquifers

with lower permeabilities, such as the crystalline rocks, generally showed a greater frequency

of detection; however, the number of samples

from the unconsolidated sediments aquifer type

was small and may not be representative. The

unconsolidated sediments aquifer is used less

than others in the RFG-use area.

MTBE Detections and Concentrations

Among Land-Use Categories

The samples were identified as being from

urban, agricultural, or forested land use on the

basis of the location of the sample site in the

land-cover data set for Pennsylvania, which is

commonly referred to as the Multi-Resolution
16

Figure 7. MTBE detections and major aquifer types in Pennsylvania (Major aquifer types modified from Berg

and others, 1980; Soller and Packard, 1998; and Lindsey and Bickford, 1999). (The minimum reporting limit is

0.2 μg/L.)
17

Figure 8. MTBE concentrations and detection frequency by carbonate rock, crystalline rock, siliciclastic rock, and unconsolidated se

near-source and ambient ground-water samples. (The minimum reporting limit is 0.2 μg/L; values below minimum reporting limit are 
18

Land Cover data set (fig. 9). The land-cover data

set was produced as a cooperative effort between

the USGS and the USEPA using data purchased

by the multi-federal-agency Multi-Resolution

Land Characterization (MLRC) Consortium. The

data were compiled from satellite imagery circa

1992 with a spatial resolution of 30 m (U.S. Geological Survey, 1992).

MTBE detections do not significantly differ

among land-use categories for near-source samples; however, frequency of MTBE detection in

ambient samples is significantly greater in

urban areas than in agricultural and forested

areas based on Kruskal-Wallis statistical test

results (fig. 10). MTBE is detected more frequently in ambient urban samples (28 percent)

than in near-source urban samples (26 percent),

but the difference is not significant. The statistical test results suggest that location of the sampling site relative to a release appears to be more

significant than the surrounding land use. However, the likelihood of detecting MTBE in nearsource or ambient samples is significantly

greater in urban areas than in ambient samples

from agricultural or forested areas. This suggests further that MTBE occurrence is linked to

urban land use.

Figure 9. MTBE ground-water sample sites and MTBE detections among land-use categories. (Landuse/land-cover data from U.S. Geological Survey, 1992.)
19

Figure 10. MTBE concentrations and detection frequency in agricultural, forest, and urban land-use categories for near-source and samples. (The minimum reporting limit is 0.2 μg/L; values below minimum reporting limit are plotted as 0.19 μg/L.)
20

Three points suggest further that high

MTBE detections in ground water are linked to

urban areas, although statistical tests do not

confirm it in this study.

1. There may be a bias in the land-cover

data for forested areas over urban areas

where canopy is mature. Near-source

samples in forested areas have MTBE

detections more frequently (22 percent)

than all other groups except the nearsource urban and the ambient urban samples. The samples that are considered to

be from forested areas may well be from

urban, suburban, or small areas of clustered population in a rural setting. None

of the 86 samples actually was collected

from a well in a forest area where there

are few people and storage tanks. Many

rural areas in Pennsylvania have sufficient tree canopy to be labeled as forested

area by the land-cover data set and may

be small towns or villages with gas stations and other commercial activities

present in a small area, where the houses

commonly are surrounded by a mature

tree canopy.

2. Wells could not be located to sample in

some urban areas in Pennsylvania where

there is high release density (figs. 2

and 9). These areas included the WilkesBarre–Scranton area, the Pittsburgh city

area, the Allentown area, and the Harrisburg city area.

3. The detection frequency of MTBE in samples from urban areas in Pennsylvania

was high and exceeded that in samples

collected nationwide for the NAWQA Program. MTBE was detected in about

14 percent of wells sampled in urban

areas for the NAWQA Program during

1991 to 2000, which had an MRL of

0.2 μg/L (Zogorski and others, 2001).

MTBE detection frequency was 28 percent in ambient samples and 26 percent in

near-source samples in the current study.

Some urban areas sampled during the

NAWQA Program had much greater

detection rates of MTBE than in the overall NAWQA national database or in the

database for the current study. For example, MTBE was detected in 79 percent of

shallow wells in Denver, Colo., and in

37 percent of shallow wells in New

England (including Connecticut, Massachusetts, and Vermont) during the

1991-94 NAWQA sampling efforts

(Squillace and others, 1995). The MRL

was 0.2 μg/L. During the NAWQA study

of the Lower Susquehanna River Basin in

Pennsylvania, a detection frequency of

50 percent in an urban area (20 wells

sampled) was reported, with an MTBE

detection level of 0.06 μg/L (Lindsey and

others, 1997; Daly and Lindsey, 1997).

MTBE Detections and Concentrations in the

Reformulated Gasoline Use Area

The RFG-use area has a greater density of

release sites (fig. 1). Results from a KruskalWallis statistical test show that the MTBE

detection frequency in near-source samples in

the RFG-use area (45 percent) was significantly

greater than detection frequencies from all other

sample groupings, whether within or outside the

RFG-use area and whether the samples are

near-source or ambient (fig. 11). The detection

frequency for ambient samples in the RFG-use

area (21 percent) was significantly greater than

that of non-RFG-use area ambient samples

(7 percent). There was no significant difference

in detection frequencies between ambient samples in the RFG-use area and near-source samples in the non-RFG-use area. The MTBE

detection frequency in the RFG-use area in

Pennsylvania is three times the MTBE detection

frequency in non-RFG-use areas of Pennsylvania

for ambient samples. For near-source samples,

the MTBE detection frequency in the RFG area

of Pennsylvania is more than four times the

MTBE detection frequency in non-RFG areas of

Pennsylvania.

The frequency of detection of MTBE among

near-source samples collected in the RFG-use

area (45 percent) is greater than the MTBE

detection frequency other studies have reported

for samples within RFG-use or other high

MTBE-use areas (Moran and others, 2002; State

of Maine, 1998; Zogorski and others, 1998; Sloto

and McManus, 1997). The studies reported in

Moran and others (2002), however, did not sample near known release sites. The detections of

MTBE among ambient samples in the RFG-use

area (21 percent) in this study are similar to

MTBE detections reported from nationwide data

of the NAWQA Program with an MRL of 0.2 μg/L

(Moran and others, 2002, Zogorski and others,

2001). In the NAWQA sampling program, MTBE
21

Figure 11. MTBE concentrations and detection frequency in near-source and ambient ground-water samples from Reformulated G

and non-RFG-use areas. (The minimum reporting limit is 0.2 μg/L; values below minimum reporting limit are plotted as 0.19 μg/L.)
22

was detected in about 20 percent of ambient

samples in areas designated as high MTBE-use

areas, whether they were RFG-use areas or Oxygenated Fuels Program areas. In high MTBEuse areas, the MTBE detection frequency is

about twice that of areas that do not have high

MTBE use in the NAWQA Program’s ambient

ground-water data set. The MTBE detection frequency found in non-RFG areas in Pennsylvania

in near-source samples (11 percent) and in ambient samples (7 percent) both exceed that for the

NAWQA ambient sample data (2 percent).

Results from the Maine study indicated that the

MTBE detection frequency in high-MTBE-use

areas is nearly twice the frequency of MTBE

detections in areas that do not have high MTBE

use in ambient samples (State of Maine, 1998).

The Maine study used a MRL of 0.1 μg/L. In a

study of community water supplies in the northeastern United States by Grady and Casey

(2000), MTBE detections were five times more

likely in high MTBE-use areas, but these samples included water supply from ground-water

and surface-water sources.

Several factors contribute to greater MTBE

detection rates in the RFG-use area in Pennsylvania.

1. Philadelphia, located in the RFG area,

generally has a greater percent volume of

MTBE in gasoline compared to Pittsburgh in the non-RFG area. The National

Institute for Petroleum and Energy

Research (NIPER) compiled data on various grades and blends of gasoline from

selected cities throughout the United

States (R. Clawges, U.S. Geological Survey, written commun., 2001). The NIPER

data include MTBE content, as percentage by volume, in gasoline. The NIPER

data are summarized by season of collection into winter (December through

March) and summer (all other months).

The NIPER data include many cities in

which samples may have been collected

only once, or very few times. In Pennsylvania, only two cities, Pittsburgh

(597 samples) and Philadelphia (391 samples), have had more than 3 samples collected during 1990-99. The mean percent

volume of MTBE in the samples from

Philadelphia during the 1990-99 sampling was 7.6 percent, and the median

was 7.7 percent. The maximum percent

volume reported during any seasonal

sampling effort was 16.80 percent, and

the seasonal minimum percent volume is

0 percent. The mean percent volume of

MTBE in the samples from Pittsburgh

during the 1990-99 sampling was

1.7 percent, and the median was

1.2 percent. The seasonal maximum percent volume was 13.4 percent, and the

seasonal minimum percent volume was

0 percent.

2. The RFG-use area has a greater density of

release sites compared to non-RFG-use

areas (fig. 1). The release density in the

2,200-mi2 RFG-use area is about

1.6 releases per square mile, compared to

a release density of about 0.1 release per

square mile in the non-RFG-use area. The

greater release density is likely related to

the greater population, vehicle, and storage-tank density in the RFG-use area.

3. The high density of ground-water wells in

the five-county RFG-use area contributes

to the likelihood that MTBE will be

detected in ground water because there

are many locations where ground water is

withdrawn.

In Pennsylvania, Chester County ranks as

the number one county in terms of population

served by self-supplied ground water; Bucks

County had the third highest population and

Montgomery County had the sixth highest population served by self-supplied ground water in

1995 (Pennsylvania Department of Environmental Protection, written commun., 1995).

In addition to self-supplied ground-water

use, the counties in the RFG-use area have some

of the highest populations that use ground water

from public systems in Pennsylvania. Montgomery County has the highest population served by

public-supplied ground water in Pennsylvania,

Bucks County had the fourth highest, Delaware

County had the fifth highest, and Chester

County had the eighth highest population

among the 67 counties in Pennsylvania. The

pumpage of ground water from the large number

of wells also will contribute to the movement of

MTBE. The large number of wells in these

RFG-use counties likely results in many wells

being located near urbanized areas and storagetank release sites, creating a situation of potential vulnerability to MTBE contamination.
23

MTBE content in gasoline can be high if a

town or city is near an RFG-use area and

receives the same gasoline as the RFG-use area

or if cross contamination occurs during transportation. There were many detects of MTBE in

neighboring counties to the RFG area such as

Lancaster, York, and more distant Cumberland

Counties (fig. 1). These three counties have a

large population served by ground water from

self-supplied sources. In 1995, Lancaster County

had the second highest county population in

Pennsylvania served by self-supplied ground

water, York County had the fifth highest, and

Cumberland County had the fourteenth highest

population served by self-supplied ground water.

The self-supplied ground-water use in these

three counties is similar to the usage in most of

the five counties within the RFG area.

Areas with Frequent MTBE Detections

Several factors are associated with high

MTBE detection frequencies in ground water in

Pennsylvania (table 2). The near-source areas

within about 0.5 mi downgradient of release

sites are at high risk for MTBE in ground water

(figs. 4 and 5). Samples from the RFG-use areas

had significantly higher MTBE detection frequencies than samples from non-RFG-use areas

(fig. 11). Samples in urban areas had significantly greater MTBE detection rates compared

to ambient ground-water samples in agriculture

and forest land-use categories (fig. 10). Nearsource samples from the crystalline-rock aquifer,

particularly when the sample was from the

RFG-use area, had a significantly greater MTBE

detection frequency compared to samples from

other aquifers (fig. 8). These areas—near-source

areas, the crystalline-rock aquifer, the RFG-use

area, and urban areas—appear to be more susceptible to MTBE detection in ground water in

Pennsylvania.

About 99 percent of MTBE samples collected

for this study had MTBE concentrations below

the USEPA Consumer Advisory threshold of

20 μg/L (for taste and odor prevention). This

study has shown, however, that MTBE detections (MTBE ≥ 0.2 μg/L) are more likely the

result of storage-tank releases than atmospheric

deposition. MTBE concentrations are likely to

increase if an MTBE plume is sampled over

time, although MTBE concentrations may also

decrease over time if attenuation has begun.

Community water system (CWS) wells in areas

at risk for MTBE detection—near releases, in

the RFG-use area, urban areas, and the crystalline-rock aquifer—could be monitored to provide

an early warning of movement of MTBE and

BTEX plumes. Many people rely on CWS wells,

which provide water year-round to at least

25 people or have a minimum of 15 residential

service connections, for drinking water supplies.

In the RFG-use area, a population of more than

600,000 depends on public water supply from

ground water. Pennsylvania has 6,696 CWS

wells, and 819 are within 0.5 mi of a release site

or within 0.5 mi of a well where MTBE was

detected in Pennsylvania (fig. 12).

Table 2. MTBE detection frequency in ground water statewide, and by RFG-use, land-use, and aquifer-type categories

Location of

wells

sampled

Detection frequency, in percent

Statewide

RFG usage Land use Aquifer type

RFG

area

Non-RFG

area

Agricultural Forested Urban CarbonateCrystallineSiliciclasticUnconsolidated

Near source 22 45 11 19 22 26 10 57 11 13

Ambient 11 21 7 8 11 28 14 18 8 0
24

SUMMARY AND CONCLUSIONS

Methyl tert-butyl-ether (MTBE) is a gasoline

additive that is used in Reformulated Gasoline

(RFG) in areas that do not meet National Ambient Air Quality Standards for carbon monoxide

and ozone. The U.S. Environmental Protection

Agency (USEPA) has issued a consumer advisory that recommends control levels of 20 to

40 μg/L of MTBE to prevent adverse odor and

taste effects and is investigating the toxicity

threat to human health. Because of its use in

gasoline as an octane enhancer, MTBE can be

detected near most leaking underground gasoline storage tanks. Thousands of releases from

leaking storage tanks have been reported to the

Pennsylvania Department of Environmental

Protection (PADEP). MTBE has high solubility

and mobility and low biodegradation properties

in water and, therefore, can be more persistent

and travel greater distances in ground water

than other gasoline constituents such as benzene, toluene, ethyl benzene, and xylene (BTEX)

compounds. MTBE has been reported in wells

used for drinking water in many areas of Pennsylvania but it is most commonly reported in the

five southeastern counties (Bucks, Chester, Delaware, Montgomery, and Philadelphia) that use

RFG to reduce year-round ozone levels.

Figure 12. Community water system wells near either storage-tank releases or sample sites with MTBE

detections. (Minimum reporting limit is 0.2 μg/L.)
25

This study, which was done in cooperation

with PADEP, examined the distribution and concentrations of MTBE in Pennsylvania’s ground

water used for drinking water supply. MTBE

concentrations and detection frequency from two

sources of MTBE in ground water, the atmosphere and storage-tank release sites (release

sites), also were examined. MTBE in ground

water was reported as detected when concentrations were at or above the minimum reporting

limit (MRL) or 0.2 μg/L. MTBE in the atmosphere was reported by the PADEP Air Quality

Bureau as detected when concentrations were at

or above the quantitation limit, which ranged

from 0.01 to 0.02 parts per billion by volume

(ppbv). The study also compared MTBE concentrations between 86 samples collected near

release sites and 359 samples collected from

ambient ground water (ground water not

thought to be associated with point-source

releases of MTBE or BTEX compounds) and

examined whether factors, such as aquifer types,

land use, or RFG-use areas were associated with

elevated MTBE occurrence in the ambient and

release sites sample sets.

Atmospheric deposition is a source of MTBE

commonly associated with low concentrations of

MTBE in ground water, but data from this study

suggest that MTBE concentrations above the

MRL (0.2 μg/L) are likely from point sources

such as release sites. Although atmospheric deposition is one of the most likely forms of nonpoint

sources for MTBE in ground water, analysis of

atmospheric MTBE data shows that most atmospheric contributions to ground water, when calculated as equivalent aqueous concentrations of

MTBE, would amount to less than the MRL used

for MTBE in ground water in this study.

Release sites are a major source of MTBE to

ground water. To evaluate release sites, groundwater samples from near these sites were compared to ambient ground-water samples. The

MTBE detection frequency for near-source samples (22 percent) was significantly greater than

the MTBE detection frequency for the ambient

samples (11 percent). The MTBE concentrations

examined in this study ranged from 0.2 to

51 μg/L. MTBE was detected at levels greater

than the USEPA Consumer Advisory threshold

of 20 μg/L in only one near-source sample and

one ambient sample.

Among the four generalized aquifer types

(carbonate rock, crystalline rock, siliciclastic

rock, and unconsolidated sediments), MTBE

detection frequency for near-source samples in

crystalline-rock aquifers (57 percent) was significantly greater than in other aquifer types. Properties of the crystalline-rock aquifers, and the

low permeability of the overlying saprolite, may

slow movement of the MTBE and result in

MTBE detections near release sites for a longer

time period than in aquifers of higher permeability. Another factor, however, may also be

involved in the high frequency of MTBE detections in the crystalline-rock aquifers. Forty percent of the total area of the crystalline aquifer

type exists within the boundary of the RFG-use

area, compared to 3, 3, and 12 percent for the

carbonate, siliciclastic, and unconsolidated sediments aquifer types, respectively.

The MTBE detection frequency in urban

areas, whether near-source or ambient samples,

is significantly greater than the MTBE detection

frequency in ambient samples in forested and

agricultural land-use areas. MTBE was detected

in 28 percent of ambient samples and in

26 percent of near-source samples in urban

areas.

The MTBE detection frequency in nearsource samples (45 percent) in the RFG-use area

is significantly greater than the detection frequency from all other sample groups whether

within or outside of the RFG-use area and

whether ambient samples or near-source samples. The detection frequency for ambient samples in the RFG-use area (21 percent) is

significantly greater than the MTBE detection

frequency for ambient samples in non-RFG-use

areas (7 percent). Several factors may contribute

to greater MTBE detection frequency in the

RFG-use area compared to the non-RFG-use

area: (1) greater volume of MTBE in gasoline,

(2) greater density of storage-tank releases,

(3) large population using ground water,

(4) large number of vehicles, and (5) greater storage-tank density.

Areas within 0.5 mi of release sites, the

RFG-use area, crystalline-rock aquifers, and

urban areas are areas of elevated risk for high

MTBE detection frequency in ground water in

Pennsylvania. Development of a network using

CWS wells, which provide a population of

600,000 in the RFG area with public water supply, to monitor MTBE concentrations in the

areas of high MTBE detection frequency could

provide early warning of migration of MTBE

plumes.
26

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29

APPENDIX 1—Concentrations of MTBE in ambient ground-water samples,

in wells near storage-tank release sites, and in atmospheric samples

Table 1A. Identification number, RFG area location, aquifer type, land-use group, MTBE concentration, and well-depth data from ambient ground-water samples in Pennsylvania

1B. Identification number, RFG area location, aquifer type, land-use group, MTBE concentration, and well-depth data from wells sampled near storage-tank releases

1C. Collection date, lab quality code, atmospheric MTBE concentration, mean daily temperature, and calculated equivalent aqueous MTBE concentration for four Air Quality Monitoring sites of the Pennsylvania Department of Environmental Protection
30

Table 1A. Identification number, RFG area location, aquifer type, land-use group, MTBE concentration, and well-depth

data from ambient ground-water samples in Pennsylvania

[μg/L, micrograms per liter; <, less than; --, unknown]

Local identification

number

Location within

RFG area

Yes / No1

Aquifer type2 Land use /

Land cover3

MTBE

(μg/L)4

Well depth

(feet below

land surface)

CH 6401 Yes Crystalline rocks agriculture <0.2 220

CH 6404 Yes Crystalline rocks agriculture <.2 50

FR 537 No Carbonate rocks agriculture <.2 65

CH 1730 Yes Crystalline rocks agriculture <.2 54

YO 1197 No Crystalline rocks agriculture <.2 140

CH 6403 Yes Crystalline rocks agriculture <.2 120

CH 5450 Yes Crystalline rocks agriculture <.2 302

CH 5477 Yes Crystalline rocks agriculture <.2 345

YO 1208 No Crystalline rocks agriculture <.2 200

AD 653 No Carbonate rocks agriculture <.2 150

YO 1206 No Crystalline rocks agriculture <.2 140

YO 1198 No Crystalline rocks agriculture <.2 125

CH 4808 Yes Crystalline rocks agriculture <.2 125

CH 4807 Yes Crystalline rocks agriculture <.2 --

FR 807 No Carbonate rocks agriculture <.2 255

CH 4345 Yes Crystalline rocks agriculture <.2 100

CH 5562 Yes Crystalline rocks urban <.2 250

CH 5479 Yes Crystalline rocks agriculture <.2 105

CH 4551 Yes Crystalline rocks agriculture 1.0 100

CH 5555 Yes Crystalline rocks urban <.2 126

CH 5474 Yes Crystalline rocks agriculture <.2 --

CH 5471 Yes Crystalline rocks forest <.2 --

FR 811 No Carbonate rocks agriculture <.2 75

LN 2052 No Crystalline rocks agriculture <.2 180

CH 5478 Yes Crystalline rocks agriculture .2 325

SO 851 No Siliciclastic rocks forest <.2 44

CH 4809 Yes Crystalline rocks agriculture <.2 --

AD 691 No Siliciclastic rocks agriculture 18.0 175

CH 2769 Yes Crystalline rocks agriculture <.2 --

AD 660 No Siliciclastic rocks urban <.2 167

YO 1194 No Carbonate rocks agriculture <.2 140

AD 690 No Siliciclastic rocks forest <.2 298

CH 6407 Yes Crystalline rocks agriculture <.2 325

SO 124 No Siliciclastic rocks agriculture <.2 75

FA 509 No Siliciclastic rocks forest <.2 200

CH 2033 Yes Crystalline rocks agriculture .8 84

CH 6405 Yes Crystalline rocks forest <.2 --

CH 5559 Yes Crystalline rocks agriculture <.2 200

CH 2311 Yes Crystalline rocks agriculture <.2 88

CH 5480 Yes Crystalline rocks urban .3 166

YO 1195 No Carbonate rocks agriculture 1.3 160

LN 2049 No Crystalline rocks forest <.2 186

YO 1201 No Crystalline rocks agriculture <.2 170

SO 852 No Siliciclastic rocks agriculture <.2 70

CH 5259 Yes Crystalline rocks forest <.2 --

CH 5260 Yes Crystalline rocks forest <.2 --

CH 5261 Yes Crystalline rocks urban <.2 --
31

FA 507 No Siliciclastic rocks urban <0.2 65

FR 808 No Carbonate rocks agriculture <.2 85

BD 530 No Carbonate rocks agriculture <.2 100

CH 5220 Yes Crystalline rocks urban <.2 --

CH 5090 Yes Crystalline rocks agriculture .5 --

CH 5475 Yes Crystalline rocks agriculture .8 --

GR 903 No Unconsolidated sediments forest <.2 125

LN 2022 No Carbonate rocks agriculture <.2 75

CH 5160 Yes Crystalline rocks forest .2 --

LN 2012 No Carbonate rocks agriculture <.2 175

LN 2011 No Carbonate rocks agriculture <.2 200

LN 2013 No Carbonate rocks agriculture <.2 150

CH 4779 Yes Crystalline rocks forest <.2 24

CH 5472 Yes Crystalline rocks forest <.2 95

CH 5563 Yes Crystalline rocks agriculture <.2 145

CH 5227 Yes Crystalline rocks forest <.2 --

FR 812 No Carbonate rocks agriculture <.2 200

LN 2021 No Carbonate rocks agriculture <.2 150

LN 2023 No Carbonate rocks agriculture <.2 175

CH 4778 Yes Crystalline rocks agriculture .5 170

LN 2026 No Carbonate rocks agriculture <.2 175

YO 1196 No Carbonate rocks agriculture <.2 200

CH 4772 Yes Crystalline rocks forest <.2 73.5

LN 2010 No Carbonate rocks agriculture <.2 175

CH 4802 Yes Carbonate rocks urban <.2 250

CH 5091 Yes Crystalline rocks forest <.2 98

CH 6400 Yes Crystalline rocks forest <.2 120

CH 4261 Yes Crystalline rocks agriculture <.2 100

CH 1110 Yes Crystalline rocks forest <.2 --

CH 5938 Yes Crystalline rocks forest <.2 430

CH 4771 Yes Crystalline rocks forest 1.1 210

CH 4767 Yes Crystalline rocks forest .3 217

LN 2025 No Carbonate rocks agriculture <.2 200

CH 5089 Yes Crystalline rocks agriculture <.2 51

CH 4573 Yes Crystalline rocks agriculture <.2 65

CH 5088 Yes Crystalline rocks agriculture 2.0 --

CH 5087 Yes Crystalline rocks urban <.2 96

CH 4828 Yes Carbonate rocks urban <.2 125

SO 125 No Siliciclastic rocks forest <.2 85

CH 5473 Yes Crystalline rocks forest <.2 75

CH 3859 Yes Carbonate rocks urban .3 --

CH 5243 Yes Crystalline rocks urban <.2 --

CH 5244 Yes Crystalline rocks urban .5 --

CH 5238 Yes Crystalline rocks forest <.2 170

CH 4539 Yes Crystalline rocks agriculture <.2 --

LN 2027 No Carbonate rocks agriculture .5 175

YO 1202 No Crystalline rocks agriculture <.2 140

Table 1A. Identification number, RFG area location, aquifer type, land-use group, MTBE concentration, and well-depth

data from ambient ground-water samples in Pennsylvania—Continued

[μg/L, micrograms per liter; <, less than; --, unknown]

Local identification

number

Location within

RFG area

Yes / No1

Aquifer type2 Land use /

Land cover3

MTBE

(μg/L)4

Well depth

(feet below

land surface)
32

CH 4339 Yes Crystalline rocks agriculture <0.2 120

CH 4805 Yes Carbonate rocks agriculture <.2 210

CH 2543 Yes Carbonate rocks forest <.2 60

FA 506 No Siliciclastic rocks forest <.2 175

CU 907 No Carbonate rocks agriculture <.2 129

LN 2024 No Carbonate rocks agriculture <.2 150

CH 245 Yes Crystalline rocks forest <.2 560

LN 2031 No Carbonate rocks agriculture <.2 150

CH 2402 Yes Carbonate rocks forest .9 --

CH 4804 Yes Carbonate rocks forest <.2 82

CU 675 No Carbonate rocks urban 51.0 150

LN 2014 No Carbonate rocks agriculture <.2 195

CH 2611 Yes Carbonate rocks forest <.2 --

CH 2676 Yes Carbonate rocks forest <.2 --

CH 202 Yes Carbonate rocks forest <.2 --

CH 204 Yes Carbonate rocks forest <.2 170

LN 2028 No Carbonate rocks agriculture <.2 200

FA 508 No Siliciclastic rocks agriculture <.2 135

CH 4815 Yes Crystalline rocks agriculture .4 90

LN 2009 No Carbonate rocks agriculture <.2 175

SO 853 No Siliciclastic rocks forest <.2 115

CU 908 No Carbonate rocks agriculture <.2 182

CH 5996 Yes Crystalline rocks agriculture <.2 120

CH 1281 Yes Crystalline rocks agriculture <.2 94

CH 4817 Yes Crystalline rocks agriculture <.2 --

LN 2008 No Carbonate rocks agriculture <.2 175

CH 5481 Yes Crystalline rocks forest <.2 --

LN 2007 No Carbonate rocks agriculture <.2 150

LN 2005 No Carbonate rocks agriculture .5 100

CH 5995 Yes Crystalline rocks forest <.2 --

MG 1399 Yes Siliciclastic rocks forest <.2 500

MG 1395 Yes Siliciclastic rocks forest <.2 530

MG 1397 Yes Siliciclastic rocks agriculture <.2 --

MG 1400 Yes Siliciclastic rocks urban <.2 497

CH 5554 Yes Crystalline rocks forest <.2 133

MG 1163 Yes Siliciclastic rocks urban .3 190

MG 1408 Yes Siliciclastic rocks urban <.2 --

MG 1390 Yes Siliciclastic rocks agriculture 1.1 --

MG 1403 Yes Siliciclastic rocks urban <.2 282

MG 1162 Yes Siliciclastic rocks urban <.2 145

MG 1161 Yes Siliciclastic rocks urban <.2 298

MG 1368 Yes Siliciclastic rocks urban <.2 --

MG 1392 Yes Siliciclastic rocks urban <.2 222

MG 1384 Yes Siliciclastic rocks forest <.2 --

MG 1393 Yes Siliciclastic rocks urban 2.6 --

LN 2015 No Carbonate rocks agriculture <.2 150

MG 1409 Yes Siliciclastic rocks forest .6 120

Table 1A. Identification number, RFG area location, aquifer type, land-use group, MTBE concentration, and well-depth

data from ambient ground-water samples in Pennsylvania—Continued

[μg/L, micrograms per liter; <, less than; --, unknown]

Local identification

number

Location within

RFG area

Yes / No1

Aquifer type2 Land use /

Land cover3

MTBE

(μg/L)4

Well depth

(feet below

land surface)
33

MG 1404 Yes Siliciclastic rocks urban <0.2 207

MG 1405 Yes Siliciclastic rocks forest 3.3 85

MG 1410 Yes Siliciclastic rocks forest <.2 --

CH 1435 Yes Crystalline rocks agriculture <.2 85

MG 1352 Yes Siliciclastic rocks forest <.2 147

LN 2019 No Carbonate rocks agriculture <.2 200

MG 1412 Yes Siliciclastic rocks forest <.2 170

CH 4498 Yes Siliciclastic rocks urban 9.1 --

LN 2006 No Carbonate rocks agriculture <.2 125

CH 1283 Yes Crystalline rocks agriculture <.2 90

LN 2029 No Carbonate rocks agriculture .3 140

MG 1411 Yes Siliciclastic rocks forest <.2 225

CU 913 No Carbonate rocks agriculture <.2 162

MG 225 Yes Siliciclastic rocks urban <.2 486

LN 2030 No Carbonate rocks agriculture <.2 97

MG 1724 Yes Siliciclastic rocks forest <.2 92

LN 2018 No Carbonate rocks agriculture <.2 160

FR 810 No Carbonate rocks agriculture <.2 90

WE 312 No Siliciclastic rocks agriculture <.2 150

CU 912 No Carbonate rocks agriculture <.2 162

CU 915 No Carbonate rocks agriculture <.2 160

CH 5269 Yes Siliciclastic rocks urban <.2 97

CH 5272 Yes Siliciclastic rocks urban <.2 --

CH 5270 Yes Siliciclastic rocks agriculture .5 85

CU 926 No Carbonate rocks agriculture <.2 100

CH 5556 Yes Siliciclastic rocks forest <.2 217

CU 922 No Carbonate rocks agriculture <.2 120

WE 309 No Siliciclastic rocks agriculture <.2 55

CH 1567 Yes Siliciclastic rocks agriculture <.2 105

CH 4409 Yes Siliciclastic rocks forest 5.1 65.7

CH 2317 Yes Crystalline rocks forest <.2 86

CU 923 No Carbonate rocks agriculture <.2 225

CH 4803 Yes Siliciclastic rocks agriculture <.2 108

WS 973 No Siliciclastic rocks agriculture <.2 98

WE 310 No Siliciclastic rocks forest <.2 250

LN 2016 No Carbonate rocks agriculture <.2 122

CU 911 No Carbonate rocks agriculture <.2 176

CU 918 No Carbonate rocks forest <.2 203

MG 1713 Yes Siliciclastic rocks forest <.2 240

CU 904 No Carbonate rocks urban 5.9 200

CU 903 No Carbonate rocks urban <.2 170

CU 905 No Carbonate rocks urban <.2 125

WE 313 No Siliciclastic rocks forest <.2 135

CH 4801 Yes Siliciclastic rocks forest <.2 120

CU 921 No Carbonate rocks agriculture <.2 62

MG 1712 Yes Siliciclastic rocks agriculture <.2 150

CU 898 No Carbonate rocks agriculture <.2 30

Table 1A. Identification number, RFG area location, aquifer type, land-use group, MTBE concentration, and well-depth

data from ambient ground-water samples in Pennsylvania—Continued

[μg/L, micrograms per liter; <, less than; --, unknown]

Local identification

number

Location within

RFG area

Yes / No1

Aquifer type2 Land use /

Land cover3

MTBE

(μg/L)4

Well depth

(feet below

land surface)
34

LN 2017 No Carbonate rocks agriculture <0.2 160

CU 278 No Carbonate rocks urban .2 116

MG 1726 Yes Siliciclastic rocks agriculture <.2 93.4

SO 126 No Siliciclastic rocks forest <.2 114

CU 902 No Carbonate rocks urban <.2 41.1

CU 899 No Carbonate rocks urban <.2 42

CU 901 No Carbonate rocks urban .8 46

CU 920 No Carbonate rocks agriculture <.2 102

MG 1714 Yes Siliciclastic rocks urban <.2 210

BE 1698 No Siliciclastic rocks agriculture <.2 95

CU 906 No Carbonate rocks urban .2 175

DA 841 No Carbonate rocks agriculture <.2 180

MG 1449 Yes Siliciclastic rocks agriculture <.2 114

DA 842 No Carbonate rocks urban <.2 61.5

CU 285 No Siliciclastic rocks urban <.2 69

DA 487 No Siliciclastic rocks urban <.2 150

DA 840 No Carbonate rocks agriculture <.2 40

DA 839 No Carbonate rocks urban <.2 50

MG 1728 Yes Siliciclastic rocks forest <.2 150

LB 1167 No Carbonate rocks agriculture <.2 158

LB 1163 No Carbonate rocks agriculture <.2 100

MG 917 Yes Siliciclastic rocks wetlands <.2 500

LB 1164 No Carbonate rocks agriculture <.2 150

LB 1166 No Carbonate rocks forest <.2 87

BE 1699 No Siliciclastic rocks agriculture <.2 260

LB 1160 No Carbonate rocks urban <.2 180

LB 1165 No Carbonate rocks agriculture <.2 115

LB 1162 No Carbonate rocks agriculture <.2 220

LB 1159 No Carbonate rocks urban 4.0 48.9

PE 676 No Siliciclastic rocks forest <.2 120

LB 1157 No Carbonate rocks agriculture <.2 100

LB 1158 No Carbonate rocks urban <.2 149

LB 1156 No Carbonate rocks urban .4 225

PE 678 No Siliciclastic rocks agriculture <.2 140

PE 677 No Siliciclastic rocks forest <.2 165

AG 714 No Siliciclastic rocks forest <.2 55

WE 413 No Siliciclastic rocks agriculture <.2 140

MG 1715 Yes Siliciclastic rocks agriculture <.2 200

PE 682 No Siliciclastic rocks forest <.2 140

PE 679 No Siliciclastic rocks agriculture <.2 200

DA 830 No Siliciclastic rocks forest <.2 160

BE 1708 No Carbonate rocks agriculture <.2 175

BE 1707 No Siliciclastic rocks agriculture <.2 90

IN 915 No Siliciclastic rocks forest <.2 95

DA 833 No Siliciclastic rocks agriculture <.2 200

PE 681 No Siliciclastic rocks forest <.2 100

PE 680 No Siliciclastic rocks forest <.2 200

Table 1A. Identification number, RFG area location, aquifer type, land-use group, MTBE concentration, and well-depth

data from ambient ground-water samples in Pennsylvania—Continued

[μg/L, micrograms per liter; <, less than; --, unknown]

Local identification

number

Location within

RFG area

Yes / No1

Aquifer type2 Land use /

Land cover3

MTBE

(μg/L)4

Well depth

(feet below

land surface)
35

WE 315 No Siliciclastic rocks forest <0.2 30

IN 914 No Siliciclastic rocks agriculture <.2 160

BE 1617 No Siliciclastic rocks agriculture <.2 128

DA 832 No Siliciclastic rocks agriculture <.2 80

LE 1418 No Siliciclastic rocks agriculture <.2 400

LB 1155 No Siliciclastic rocks forest <.2 96

DA 834 No Siliciclastic rocks forest <.2 200

MF 402 No Carbonate rocks agriculture <.2 102

AG 705 No Siliciclastic rocks forest <.2 215

WE 311 No Siliciclastic rocks forest <.2 220

BE 1703 No Siliciclastic rocks agriculture <.2 120

PE 683 No Siliciclastic rocks agriculture <.2 173

DA 836 No Siliciclastic rocks agriculture <.2 120

SC 634 No Siliciclastic rocks agriculture <.2 120

SC 613 No Siliciclastic rocks agriculture <.2 200

HU 421 No Carbonate rocks agriculture <.2 65

DA 835 No Siliciclastic rocks agriculture <.2 150

JU 369 No Siliciclastic rocks agriculture <.2 125

BE 1704 No Siliciclastic rocks agriculture <.2 300

JU 370 No Siliciclastic rocks agriculture <.2 150

IN 917 No Siliciclastic rocks forest <.2 82

DA 837 No Siliciclastic rocks agriculture <.2 200

NU 520 No Siliciclastic rocks agriculture <.2 155

AR 106 No Unconsolidated sediments agriculture <.2 55

BE 1705 No Siliciclastic rocks forest <.2 245

SC 614 No Siliciclastic rocks agriculture <.2 120

SC 637 No Siliciclastic rocks forest <.2 164

MF 404 No Carbonate rocks agriculture <.2 200

SN 245 No Siliciclastic rocks agriculture <.2 100

SN 246 No Siliciclastic rocks agriculture <.2 200

AR 105 No Siliciclastic rocks agriculture <.2 110

LE 1420 No Siliciclastic rocks agriculture <.2 130

SC 615 No Siliciclastic rocks agriculture <.2 180

LE 1419 No Siliciclastic rocks agriculture <.2 220

IN 861 No Siliciclastic rocks agriculture <.2 85

NU 524 No Siliciclastic rocks agriculture <.2 205

SC 636 No Siliciclastic rocks agriculture <.2 275

SN 249 No Siliciclastic rocks agriculture <.2 114

CE 669 No Carbonate rocks forest <.2 210

IN 913 No Siliciclastic rocks agriculture <.2 123

NU 522 No Siliciclastic rocks agriculture <.2 201

NP 816 No Siliciclastic rocks agriculture <.2 150

SC 296 No Siliciclastic rocks forest <.2 242

IN 918 No Siliciclastic rocks forest <.2 65

CB 338 No Siliciclastic rocks agriculture <.2 150

SC 635 No Siliciclastic rocks forest <.2 306

NU 523 No Siliciclastic rocks agriculture <.2 100

Table 1A. Identification number, RFG area location, aquifer type, land-use group, MTBE concentration, and well-depth

data from ambient ground-water samples in Pennsylvania—Continued

[μg/L, micrograms per liter; <, less than; --, unknown]

Local identification

number

Location within

RFG area

Yes / No1

Aquifer type2 Land use /

Land cover3

MTBE

(μg/L)4

Well depth

(feet below

land surface)
36

AR 108 No Siliciclastic rocks agriculture <0.2 100

NP 818 No Siliciclastic rocks agriculture <.2 260

IN 916 No Siliciclastic rocks forest <.2 165

SN 247 No Siliciclastic rocks agriculture <.2 199

CB 334 No Siliciclastic rocks forest <.2 440

CB 335 No Siliciclastic rocks forest <.2 220

CE 671 No Carbonate rocks agriculture <.2 200

IN 911 No Siliciclastic rocks forest <.2 --

IN 107 No Siliciclastic rocks forest <.2 124

CE 672 No Carbonate rocks agriculture <.2 200

MO 684 No Siliciclastic rocks forest <.2 260

AR 107 No Siliciclastic rocks agriculture <.2 154

CB 337 No Siliciclastic rocks agriculture <.2 500

JE 384 No Siliciclastic rocks forest <.2 --

JE 411 No Siliciclastic rocks agriculture <.2 --

JE 397 No Siliciclastic rocks agriculture <.2 --

MO 689 No Carbonate rocks agriculture <.2 64

NP 817 No Siliciclastic rocks forest <.2 200

JE 409 No Siliciclastic rocks forest <.2 --

JE 386 No Siliciclastic rocks forest <.2 --

MO 682 No Siliciclastic rocks forest <.2 340

JE 393 No Siliciclastic rocks agriculture <.2 --

JE 415 No Siliciclastic rocks forest <.2 --

JE 418 No Siliciclastic rocks quarries/mines <.2 --

JE 399 No Siliciclastic rocks forest <.2 --

JE 388 No Siliciclastic rocks agriculture <.2 --

AR 104 No Siliciclastic rocks forest <.2 60

CH 5364 Yes Siliciclastic rocks forest .3 160

JE 400 No Siliciclastic rocks agriculture <.2 --

CB 336 No Siliciclastic rocks forest .9 88

JE 389 No Siliciclastic rocks agriculture <.2 --

JE 410 No Siliciclastic rocks agriculture <.2 --

JE 395 No Siliciclastic rocks agriculture <.2 --

MO 683 No Siliciclastic rocks forest .3 160

JE 317 No Siliciclastic rocks agriculture <.2 --

JE 402 No Siliciclastic rocks agriculture <.2 --

JE 401 No Siliciclastic rocks agriculture <.2 --

CF 310 No Siliciclastic rocks forest <.2 --

CR 725 No Siliciclastic rocks forest <.2 30

JE 417 No Siliciclastic rocks forest <.2 --

JE 407 No Siliciclastic rocks forest <.2 --

JE 406 No Siliciclastic rocks forest <.2 --

CR 726 No Siliciclastic rocks quarries/mines <.2 70

JE 422 No Siliciclastic rocks agriculture <.2 60

CR 723 No Siliciclastic rocks agriculture <.2 80

CF 309 No Siliciclastic rocks agriculture <.2 --

CF 314 No Siliciclastic rocks forest <.2 --

Table 1A. Identification number, RFG area location, aquifer type, land-use group, MTBE concentration, and well-depth

data from ambient ground-water samples in Pennsylvania—Continued

[μg/L, micrograms per liter; <, less than; --, unknown]

Local identification

number

Location within

RFG area

Yes / No1

Aquifer type2 Land use /

Land cover3

MTBE

(μg/L)4

Well depth

(feet below

land surface)
37

JE 405 No Siliciclastic rocks transitional <0.2 --

CF 320 No Siliciclastic rocks forest .3 110

JE 423 No Siliciclastic rocks agriculture <.2 98

PI 308 No Unconsolidated sediments forest <.2 108

JE 424 No Siliciclastic rocks agriculture <.2 50

PI 520 No Unconsolidated sediments urban <.2 200

CR 727 No Siliciclastic rocks forest <.2 178

VE 58 No Siliciclastic rocks agriculture <.2 63

JE 421 No Siliciclastic rocks agriculture <.2 75

CR 722 No Siliciclastic rocks forest <.2 58

PI 480 No Unconsolidated sediments forest <.2 213

CR 724 No Siliciclastic rocks agriculture <.2 120

PI 519 No Siliciclastic rocks forest .7 120

CW 2409 No Siliciclastic rocks urban <.2 60

CW 2415 No Siliciclastic rocks agriculture <.2 35

CW 2410 No Siliciclastic rocks agriculture <.2 172

CW 2414 No Siliciclastic rocks wetlands <.2 32

CW 2411 No Siliciclastic rocks forest <.2 110

CW 2413 No Siliciclastic rocks forest <.2 75

CW 2412 No Unconsolidated sediments agriculture <.2 90

WN 209 No Siliciclastic rocks forest <.2 142

WR 835 No Siliciclastic rocks transitional <.2 50

MC 123 No Siliciclastic rocks agriculture <.2 130

ER 7001 No Unconsolidated sediments forest <.2 68

ER 2501 No Siliciclastic rocks agriculture <.2 170

ER 5003 No Unconsolidated sediments agriculture <.2 87

WR 836 No Unconsolidated sediments agriculture <.2 60

MC 124 No Unconsolidated sediments agriculture <.2 135

ER 2004 No Siliciclastic rocks agriculture <.2 80

ER 4007 No Siliciclastic rocks forest <.2 130

1 RFG is the Reformulated Gasoline-use area that consists of five counties (Bucks, Chester, Delaware, Montgomery, and

Philadelphia) in Pennsylvania. 2 Aquifer type is determined by intersection of well location with generalized aquifer digital spatial information data set (Lindsey

and Bickford, 1999).

3 Land use / land cover is determined by intersection of well location with USGS digital spatial information data set on land

use/land cover (U.S. Geological Survey, 1992). 4 Minimum reporting level (MRL) used for data in this report is 0.2 μg/L. MTBE concentrations are rounded to nearest tenth of a

microgram.

Table 1A. Identification number, RFG area location, aquifer type, land-use group, MTBE concentration, and well-depth

data from ambient ground-water samples in Pennsylvania—Continued

[μg/L, micrograms per liter; <, less than; --, unknown]

Local identification

number

Location within

RFG area

Yes / No1

Aquifer type2 Land use /

Land cover3

MTBE

(μg/L)4

Well depth

(feet below

land surface)
38

Table 1B. Identification number, RFG area location, aquifer type, land-use group, MTBE concentration, and welldepth data from wells sampled near storage tank releases

[<, less than; μg/L, micrograms per liter; --, unknown]

Local identification

number

Location

within

RFG-use

area1

Aquifer type2 Land use/

land cover3

MTBE,

(μg/L)4

Well depth,

in feet below

land surface

CH 6509 Yes crystalline rock forest <0.2 200

AD 1072 No crystalline rock forest <.2 125

AD 1073 No carbonate rock agriculture <.2 143

CH 6506 Yes crystalline rock urban .2 250

DE 855 Yes crystalline rock forest 1.0 110

DE 484 Yes unconsolidated sediments urban <.2 100

CH 6508 Yes crystalline rock forest <.2 100

CH 6507 Yes crystalline rock forest <.2 258

CH 1134 Yes crystalline rock forest .3 120

CH 104 Yes crystalline rock urban <.2 55

DE 862 Yes crystalline rock forest <.2 --

DE 791 Yes crystalline rock forest <.2 180

CH 6497 Yes crystalline rock forest .5 100

SO 855 No siliciclastic rock forest <.2 47

CH 6512 Yes crystalline rock forest .3 100

LN 2110 No carbonate rock agriculture .3 36

CH 5446 Yes crystalline rock forest <.2 285

CH 6510 Yes crystalline rock forest <.2 260

CH 6511 Yes crystalline rock forest .4 85

LN 2107 No carbonate rock forest <.2 400

LN 2109 No carbonate rock urban <.2 80

CH 2634 Yes carbonate rock agriculture <.2 110

PH 1039 Yes unconsolidated sediments urban .2 26

CH 5052 Yes crystalline rock agriculture .6 120

BK 3000 Yes unconsolidated sediments urban .6 90

MG 1908 Yes carbonate rock urban 13.4 400

LN 2112 No carbonate rock agriculture <.2 162

LN 2106 No crystalline rock agriculture .4 200

LN 2108 No carbonate rock agriculture <.2 44

BK 2787 Yes crystalline rock urban 5.6 37

BK 2997 Yes crystalline rock urban .3 180

DA 527 No crystalline rock agriculture .4 300

LN 2111 No carbonate rock agriculture <.2 40

LN 2104 No siliciclastic rock urban <.2 80

MG 1674 Yes siliciclastic rock forest <.2 285

MG 958 Yes siliciclastic rock urban <.2 271

CU 950 No carbonate rock agriculture <.2 180

CU 949 No carbonate rock agriculture <.2 175

MG 1761 Yes siliciclastic rock agriculture <.2 225

MG 1673 Yes siliciclastic rock forest <.2 120

MG 1180 Yes siliciclastic rock urban <.2 189

WS 974 No siliciclastic rock agriculture <.2 55

BK 2998 Yes siliciclastic rock agriculture <.2 110

LB 191 No carbonate rock agriculture <.2 80

BE 1718 No carbonate rock urban <.2 223

CA 457 No siliciclastic rock forest <.2 225

BE 1426 No carbonate rock forest <.2 350
39

AG 711 No siliciclastic rock forest <0.2 108

AG 708 No siliciclastic rock forest <.2 80

BK 2999 Yes siliciclastic rock forest .4 100

BA 640 No carbonate rock urban <.2 80

BE 619 No carbonate rock urban <.2 248

BA 641 No carbonate rock forest <.2 100

AG 712 No unconsolidated sediments urban <.2 60

AG 707 No unconsolidated sediments agriculture <.2 60

LE 1424 No crystalline rock forest .7 100

AG 710 No siliciclastic rock urban <.2 131

AG 709 No siliciclastic rock forest <.2 185

LE 1422 No carbonate rock forest <.2 152

IN 920 No siliciclastic rock agriculture <.2 60

BV 226 No siliciclastic rock urban <.2 100

LE 1423 No carbonate rock urban <.2 150

NP 821 No carbonate rock agriculture <.2 110

LA 1202 No unconsolidated sediments agriculture <.2 79

LA 1203 No siliciclastic rock forest <.2 100

MO 693 No siliciclastic rock forest <.2 300

MR 3308 No unconsolidated sediments forest <.2 64

LY 684 No carbonate rock agriculture <.2 250

LY 683 No siliciclastic rock urban <.2 250

MR 3307 No unconsolidated sediments agriculture <.2 65

LY 685 No siliciclastic rock agriculture 31.9 90

WY 180 No siliciclastic rock urban <.2 200

TI 575 No siliciclastic rock urban <.2 79

WR 837 No unconsolidated sediments urban <.2 51

ER 2513 No siliciclastic rock agriculture <.2 80

ER 2512 No unconsolidated sediments agriculture <.2 45

ER 2508 No siliciclastic rock agriculture <.2 43

ER 8544 No unconsolidated sediments forest <.2 83

ER 2514 No unconsolidated sediments agriculture <.2 20

ER 2509 No siliciclastic rock forest <.2 100

ER 2505 No unconsolidated sediments urban <.2 24

ER 2507 No unconsolidated sediments urban <.2 25

ER 2510 No unconsolidated sediments forest <.2 24.1

ER 2506 No siliciclastic rock urban .2 19

ER 2515 No siliciclastic rock urban <.2 90

ER 2511 No unconsolidated sediments agriculture <.2 88

1 RFG is the Reformulated Gasoline-use area that consists of five counties (Bucks, Chester, Delaware, Montgomery, and

Philadelphia) in Pennsylvania. 2 Aquifer type is determined by intersection of well location with generalized aquifer digital spatial information data set,

after Lindsey and Bickford (1999).

3 Land use / land cover is determined by intersection of well location with USGS digital spatial information data set on

land use/land cover (U.S. Geological Survey, 1992). 4 Minimum reporting level (MRL) is 0.2 μg/L and all estimated values below 0.2 μg/L are listed as MRL. MTBE

concentrations are rounded to nearest tenth of a microgram.

Table 1B. Identification number, RFG area location, aquifer type, land-use group, MTBE concentration, and welldepth data from wells sampled near storage tank releases—Continued

[<, less than; μg/L, micrograms per liter; --, unknown]

Local identification

number

Location

within

RFG-use

area1

Aquifer type2 Land use/

land cover3

MTBE,

(μg/L)4

Well depth,

in feet below

land surface
40

Table 1C. Collection date, lab quality code, atmospheric MTBE concentration, mean daily temperature, and calculated

equivalent aqueous MTBE concentration for four Air Quality Monitoring sites of the Pennsylvania Department of

Environmental Protection

[ppbv, part per billion by volume; deg F, degrees Fahrenheit; μg/L, micrograms per liter; --, missing data]

Date

collected1

West Chester Pittsburgh

Quality

code2

Atmospheric

MTBE

(ppbv)3

Mean

daily

temperature

(deg F)4

Equivalent

aqueous

MTBE

(μg/L)5

Quality

code2

Atmospheric

MTBE

(ppbv)6

Mean

daily

temperature

(deg F)7

Equivalent

aqueous

MTBE

(μg/L)5

4/1/01 — 0.33 43 0.298 J 0.06 41.2 0.055

4/7/01 — .83 47 .460 J .05 68.2 .011

4/13/01 — .39 62 .132 U .01 61.7 .003

4/19/01 — .25 41 .224 — .12 41.4 .104

4/25/01 — .23 47 .126 J .04 46.5 .020

5/1/01 — .28 64 .061 — .53 66.4 .114

5/7/01 — .24 51 .131 — .11 62.3 .038

5/13/01 U .02 58 .007 J .03 49.1 .017

5/19/01 — .18 65 .039 .16 65 .034

5/25/01 — .47 61 .161 J .05 56.3 .017

5/31/01 U .02 54 .011 U .01 53.4 .005

6/6/01 — .27 66 .058 — .06 63.1 .022

6/12/01 — .22 72 .046 — .22 73.1 .031

6/18/01 — .14 71 .030 — .21 68.5 .046

6/24/01 J .10 67 .022 — .17 62.5 .056

6/30/01 — .36 80 .050 — .10 75.6 .014

7/6/01 — .11 64 .023 — -- 62.7 --

7/12/01 — .15 66 .032 — -- 66.4 --

7/18/01 — .44 71 .096 U .01 74.1 .001

7/24/01 — .12 79 .017 — .09 78.8 .012

7/30/01 — -- -- -- — .08 68.8 .017

8/5/01 — .44 78 .062 — .16 77.8 .022

8/11/01 — .58 72 .125 U .01 75.8 .001

8/17/01 — .18 75 .025 U .01 71.3 .002

8/23/01 — .38 71 .082 U .01 68.5 .002

8/29/01 — .36 72 .077 — .19 68 .041

9/4/01 — .23 70 .050 U .01 71.2 .002

9/10/01 — -- -- -- U .01 70.6 .002

9/16/01 — -- -- -- J .14 57.2 .050

9/22/01 Q .27 69 .058 U .01 62.6 .003

9/28/01 — -- -- -- U .01 51.5 .005

10/4/01 — .84 65 .183 U .01 66.8 .002

10/10/01 — .58 49 .319 — .29 55.5 .100

10/16/01 — .70 52 .383 J .21 48.1 .116

10/22/01 — .43 62 .146 J .19 62.4 .064

10/28/01 — -- -- -- U .01 39.3 .010

11/3/01 — .26 59 .089 — -- 54.5 --

11/9/01 J .12 47 .066 U .01 44.4 .009

11/15/01 — .61 53 .333 U .01 57.6 .003

11/21/01 — .25 34 .228 — .28 33.9 .255

11/27/01 — .95 48 .524 — .26 48.4 .143

12/3/01 — .60 40 .540 J .17 44 .152

12/9/01 — -- -- -- U .01 39 .009

12/15/01 — -- -- -- U .01 41.1 .009
41

Table 1C. Collection date, lab quality code, atmospheric MTBE concentration, mean daily temperature, and

calculated equivalent aqueous MTBE concentration for four Air Quality Monitoring sites of the Pennsylvania

Department of Environmental Protection—Continued

[ppbv, part per billion by volume; deg F, degrees Fahrenheit; μg/L, micrograms per liter; --, missing data]

Lancaster Arendtsville

Quality

code2

Atmospheric

MTBE

(ppbv)8

Mean

daily

temperature

(deg F)4

Equivalent

aqueous

MTBE

(μg/L)5

Quality

code2

Atmospheric

MTBE

(ppbv)9

Mean

daily

temperature

(deg F)10

Equivalent

aqueous

MTBE

(μg/L)5

— 0.092 41 0.082 — -- -- --

— .472 49 .260 — -- -- --

— .144 62 .049 — -- -- --

— .075 44 .067 — -- -- --

J .044 48 .024 — -- -- --

— .208 66 .045 — -- -- --

— .125 53 .068 — -- -- --

U .02 57 .007 U 0.02 59.5 0.007

— .139 67 .030 — .244 66.5 .053

— .388 62 .132 — -- -- --

U .02 57 .007 U .02 58.2 .007

U .02 68 .004 — -- -- --

— .161 75 .022 U .02 76 .003

— .064 75 .009 — -- -- --

— -- -- -- U .02 68.2 .004

— .277 81 .038 U .02 81.8 .002

— -- -- -- U .02 67.1 .004

— -- -- -- U .02 72.3 .004

— .225 72 .048 — .144 75 .020

U .02 82 .002 — .089 83.2 .008

— .128 71 .028 U .02 68.6 .004

— .128 79 .018 — -- -- --

— -- -- -- U .02 76.1 .003

— .14 77 .019 U .02 78.6 .003

— .21 71 .045 U .02 72.5 .004

U .02 75 .003 U .02 73.9 .003

— -- -- -- — -- -- --

— .11 72 .024 — -- -- --

J .16 58 .055 — -- -- --

J .17 70 .037 U .02 70.9 .004

U .02 53 .011 U .02 53.1 .011

Q .28 67 .061 U .02 67.4 .004

J .23 53 .126 U .02 51.7 .011

J .14 51 .077 — -- -- --

J .17 62 .058 U .02 60.2 .007

— -- -- -- U .02 42.9 .018

J .12 62 .041 U .02 64.9 .004

U .02 48 .011 U .02 52.9 .011

— .49 52 .268 U .02 52 .011

J .13 37 .118 U .02 36.7 .018

— .3 48 .166 J .21 46.2 .116

— .26 40 .234 U .02 41.2 .018

J .15 39 .135 U .02 40.9 .018

U .02 42 .018 U .02 48.4 .011
42

12/21/01 — -- -- -- U 0.01 30.7 0.009

12/27/01 — -- -- -- — -- -- --

1/2/02 — -- -- -- — -- -- --

1/8/02 — -- -- -- — -- -- --

1/14/02 — -- -- -- — -- -- --

1/20/02 — -- -- -- — -- -- --

1/26/02 — -- -- -- — -- -- --

2/1/02 — -- -- -- — -- -- --

2/7/02 — -- -- -- — -- -- --

2/13/02 — -- -- -- — -- -- --

2/19/02 — -- -- -- — -- -- --

2/25/02 — -- -- -- — -- -- --

3/3/02 — -- -- -- — -- -- --

3/9/02 — -- -- -- — -- -- --

3/15/02 — -- -- -- — -- -- --

3/21/02 — -- -- -- — -- -- --

3/27/02 — -- -- -- — -- -- --

1 Data were scheduled for collection over a 24-hour period once every 6 days.

2 PA DEP Air Quality organics laboratory quality codes are as follows:

U - Indicates compound was analyzed for but not detected. The sample quantitation limit is reported.

J - Indicates an estimated value, below the quantification limit, but above the method detection limit.

Q - This flag identifies the average of multiple results from multiple analysis, or the average of the averages of dual column analysis

methods.

— - Indicates no quality code needed.

3 West Chester air-quality sampling site is at West Chester University South campus, latitude 395624 longitude 753600.

4 Mean daily temperatures from DEP air quality monitor site.

5 See Appendix 2 for equation used to calculate equivalent aqueous MTBE concentrations.

6 Pittsburgh air quality station located at 39th and Penn Streets in Pittsburgh.

7 Mean daily temperature from NOAA data at Pittsburgh.

8Lancaster air quality data from latitude 400249 longitude 761700.

9Arendtsville data from air quality station at PSU Experimental Orchard at latitude 395525 longitude 771829.

10Mean daily temperatures from NOAA data at Harrisburg.

Table 1C. Collection date, lab quality code, atmospheric MTBE concentration, mean daily temperature, and calculated

equivalent aqueous MTBE concentration for four Air Quality Monitoring sites of the Pennsylvania Department of

Environmental Protection—Continued

[ppbv, part per billion by volume; deg F, degrees Fahrenheit; μg/L, micrograms per liter; --, missing data]

Date

collected1

West Chester Pittsburgh

Quality

code2

Atmospheric

MTBE

(ppbv)3

Mean

daily

temperature

(deg F)4

Equivalent

aqueous

MTBE

(μg/L)5

Quality

code2

Atmospheric

MTBE

(ppbv)6

Mean

daily

temperature

(deg F)7

Equivalent

aqueous

MTBE

(μg/L)5
43

U 0.02 36 0.018 U 0.02 37.8 0.018

U .02 26 .019 U .02 26.7 .018

U .02 26 .019 U .02 25.6 .019

U .02 28 .018 U .02 28.5 .018

J .092 37 .083 U .02 34.5 .018

J .1 29 .092 U .02 27.8 .018

J .1 40 .090 U .02 39.6 .018

U .02 45 .018 U .02 43.4 .018

J .23 36 .209 U .02 36.3 .018

U .02 34 .018 U .02 37.9 .018

U .02 39 .018 U .02 33.4 .018

J .13 41 .117 J .15 40.6 .135

U .02 49 .011 U .02 48.2 .011

J .035 58 .012 J .062 54.5 .034

J .12 57 .041 J .097 56.8 .033

U .02 45 .018 U .02 46.3 .011

U .02 41 .018 U .02 41.8 .018

Table 1C. Collection date, lab quality code, atmospheric MTBE concentration, mean daily temperature, and

calculated equivalent aqueous MTBE concentration for four Air Quality Monitoring sites of the Pennsylvania

Department of Environmental Protection—Continued

[ppbv, part per billion by volume; deg F, degrees Fahrenheit; μg/L, micrograms per liter; --, missing data]

Lancaster Arendtsville

Quality

code2

Atmospheric

MTBE

(ppbv)8

Mean

daily

temperature

(deg F)4

Equivalent

aqueous

MTBE

(μg/L)5

Quality

code2

Atmospheric

MTBE

(ppbv)9

Mean

daily

temperature

(deg F)10

Equivalent

aqueous

MTBE

(μg/L)5
44

Appendix 2—Equations used to calculate equivalent aqueous MTBE concentration

The equation used to calculate equivalent aqueous concentration of MTBE from atmospheric

concentration of MTBE is as follows from Baehr and others (1999, p. 131):

(1)

 where:

C is equivalent aqueous concentration of MTBE, in micrograms per liter;

ω is molecular weight of MTBE = 88.15;

A is atmospheric concentration of MTBE, in parts per billion by volume;

P is atmospheric pressure = 1.0 atmospheres;

H is Henry’s Law coefficient, dimensionless. This coefficient is temperature dependent and is

calculated according to the vann Hoff equation:

d ln (H) / dT = H Henry / RT2.

Data used for calculations in this report are from tabled data of H in Baehr and others

(1999, p.131, table 3).

R is gas constant = 8.205783 × 10-5 (meter3 atmospheres)/(moles Kelvin)

T is temperature in Kelvin degrees

C ω A PH 106 = × × ⁄ × × R T ×

∆